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At least 253 records · Page 14

All sources NASA NTRS DOE OSTI

DOE OSTI2018

Assessing Fossil Fuel and Feedstock Use in the U.S. Plastics and Rubber Sector: A Supply Chain Analysis

In plastics and rubber manufacturing, fossil fuels are consumed both as an energy source and as feedstocks that are converted to higher-value products. For example, in the manufacture of polyethylene, natural gas is consumed both as a fuel and as a feedstock during ethylene production. In this work, we expand on the U.S. Department of Energy's Bandwidth Study on Energy Use and Potential Energy Savings Opportunities in U.S. Plastics and Rubber Manufacturing, which quantified onsite fuel consumption and the potential for reducing fuel consumption by increasing energy efficiency in the plastics and rubber sector. The bandwidth study did not quantify fuel consumed upstream in the supply chain or as a feedstock; however, both contribute significantly to a plastic's total fossil fuel requirements. The U.S. Energy Information Administration's 2014 Manufacturing Energy Consumption Survey (MECS) estimates that fossil fuels consumed as feedstocks account for approximately 74% of total fossil fuel consumption in the U.S. plastic resin manufacturing sector (NAICS 325211). We employ the Materials Flows through Industry (MFI) supply chain modeling tool, developed at the National Renewable Energy Laboratory (NREL), to quantify process fuel and feedstock requirements within the supply chains of the same 10 categories of plastics and rubber commodities covered in the DOE bandwidth report. From these results, we identify supply chains that will have a high feedstock requirement even when energy efficiency is increased. We then use MFI to analyze several alternative plastics supply chains, including those utilizing biomass feedstocks and/or polyethylene terephthalate (PET) waste upcycling, to determine if these alternatives can potentially reduce both process fuel and feedstock requirements within the supply chains of interest. This presentation will include a case study comparison of supply chain energy consumption for petroleum-derived and bio-derived fiberglass reinforced plastic involving a novel waste PET upcycling technique recently discovered by NREL researchers.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2022

Freely jointed chain models with extensible links

We report analytical relations for the mechanical response of single polymer chains are valuable for modeling purposes, on both the molecular and the continuum scale. These relations can be obtained using statistical thermodynamics and an idealized single-chain model, such as the freely jointed chain model. To include bond stretching, the rigid links in the freely jointed chain model can be made extensible, but this almost always renders the model analytically intractable. Here, an asymptotically correct statistical thermodynamic theory is used to develop analytic approximations for the single-chain mechanical response of this model. The accuracy of these approximations is demonstrated using several link potential energy functions. This approach can be applied to other single-chain models, and to molecular stretching in general.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Harnessing Aromatic‐Histidine Interactions through Synergistic Backbone Extension and Side Chain Modification

Abstract Peptide engineering efforts have delivered drugs for diverse human diseases. Side chain alteration is among the most common approaches to designing new peptides for specific applications. The peptide backbone can be modified as well, but this strategy has received relatively little attention. Here we show that new and favorable contacts between a His side chain on a target protein and an aromatic side chain on a synthetic peptide ligand can be engineered by rational and coordinated side chain modification and backbone extension. Side chain modification alone was unsuccessful. Binding measurements, high‐resolution structural studies and pharmacological outcomes all support the synergy between backbone and side chain modification in engineered ligands of the parathyroid hormone receptor‐1, which is targeted by osteoporosis drugs. These results should motivate other structure‐based designs featuring coordinated side chain modification and backbone extension to enhance the engagement of peptide ligands with target proteins.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Harnessing Aromatic‐Histidine Interactions through Synergistic Backbone Extension and Side Chain Modification

36 MATERIALS SCIENCE↗

DOE OSTI2012

Studies on the production of branched-chain alcohols in engineered Ralstonia eutropha

Wild-type Ralstonia eutropha H16 produces polyhydroxybutyrate (PHB) as an intracellular carbon storage material during nutrient stress in the presence of excess carbon. In this study, the excess carbon was redirected in engineered strains from PHB storage to the production of isobutanol and 3-methyl-1-butanol (branched-chain higher alcohols). These branched-chain higher alcohols can directly substitute for fossil-based fuels and be employed within the current infrastructure. Various mutant strains of R. eutropha with isobutyraldehyde dehydrogenase activity, in combination with the overexpression of plasmid-borne, native branched-chain amino acid biosynthesis pathway genes and the overexpression of heterologous ketoisovalerate decarboxylase gene, were employed for the biosynthesis of isobutanol and 3-methyl-1-butanol. Production of these branched-chain alcohols was initiated during nitrogen or phosphorus limitation in the engineered R. eutropha. One mutant strain not only produced over 180 mg/L branched-chain alcohols in flask culture, but also was significantly more tolerant of isobutanol toxicity than wild-type R. eutropha. After the elimination of genes encoding three potential carbon sinks (ilvE, bkdAB, and aceE), the production titer improved to 270 mg/L isobutanol and 40 mg/L 3-methyl-1-butanol. Semicontinuous flask cultivation was utilized to minimize the toxicity caused by isobutanol while supplying cells with sufficient nutrients. Under this semicontinuous flask cultivation, the R. eutropha mutant grew and produced more than 14 g/L branched-chain alcohols over the duration of 50 days. These results demonstrate that R. eutropha carbon flux can be redirected from PHB to branched-chain alcohols and that engineered R. eutropha can be cultivated over prolonged periods of time for product biosynthesis.

Lu, JN↗

DOE OSTI2019

Peculiarities of Immediate Response of Respiratory Chain Enzymes in Rat Cerebral Cortex to Hypoxia

We performed a complex study of the dependence of immediate reaction of catalytic subunits in mitochondrial enzymes (NDUFV2, SDHA, Cyt b, COX1, and ATP5A) in rat cerebral cortex (the most hypoxia-sensitive tissue) on the severity and duration of hypoxia in vivo and the role of individual resistance of rats to oxygen deficiency in this process. Three types of responses to hypoxia were revealed. The immediate response of mitochondria to oxygen deficiency appeared after its drop by 30-33% relatively to normal atmosphere level. It manifested in up-regulation of NAD-dependent oxidation, i.e., activation of respiratory chain complex I. Further decrease in oxygen concentration by 50% reprogrammed the work of respiratory chain via activation of respiratory chain complex II in parallel with down-regulation of the electron transport function of the respiratory chain complex I. This response was optimal for the expression of adaptation genes and for the formation of immediate tolerance of rats to hypoxia. The greatest drop of oxygen concentration by 60-62% reversed the Krebs cycle promoting recovery of the electron transport function of respiratory chain complex I. Despite this, the energy efficiency of the respiratory chain and the potency to mobilize the rapid adaptation mechanisms degraded due to abnormalities in cytochrome segment of the respiratory chain.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2017

Effects of Diisocyanate and Polymeric Epoxidized Chain Extenders on the Properties of Recycled Poly(Lactic Acid)

Increasing demand in the use of poly(lactic acid) (PLA) leads to a debate about using potential foodstuffs for plastic production and a moral issue when starvation problem is taken into account. One of the solutions is recycling of PLA; however, recycling results in property losses during melt processing due to low thermal stability of PLA. This study focuses on using chain extenders to offset thermal degradation of recycled PLA. The effects of a diisocyanate and a polymeric epoxidized chain extender on the properties of the recycled poly(lactic acid) were investigated. In order to mimic the recycling process, PLA was subjected to thermo-mechanical degradation using a laboratory scale compounder. Chain extender type, loading and mixing time were investigated. On-line rheology and intrinsic viscosity measurements of PLA before and after chain extension confirmed that the molecular weight increased. Dynamic mechanical analysis, rheology and tensile tests revealed that the chain extenders led to a significant increase in modulus, strength and melt-viscosity. It was found that diisocyanate had slightly higher and faster chain extension reactivity than polymeric extender. Differential scanning calorimetry results showed an increase in the crystallization temperature due to the branched and extended chain structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Empirical evidence that glucan-interacting amino acid side chains within the transmembrane channel collectively facilitate cellulose synthase function

The fundamental mechanism of cellulose synthesis is widely conserved across Kingdoms and depends on cellulose synthases, which are processive, dual-function, family 2 glycosyltransferases (GT-2). These enzymes polymerize glucose on the cytoplasmic side of the plasma membrane and export the glucan chain to the cell surface through an integral transmembrane (TM) channel. Structural studies of active plant cellulose synthases (CESAs) have revealed interactions between the nascent glucan chain and the side chains of polar, charged, and aromatic amino acid residues that line the TM channel. However, the functional consequences of modifying these side chains have not been tested in vivo in CESAs or other processive GT-2s. To test this, we used an established in vivo assay based on genetic complementation of CESA5 in the moss, Physcomitrium patens. For accurate prediction of glucan-interacting amino acid residues, we generated a complete homotrimeric molecular model of PpCESA5 using a combination of homology and de novo modeling. All-atom molecular dynamics-based analyses of contact metrics and interaction energy identified 23 amino acid residues with high propensity to interact with the nascent glucan chain within the TM channel or on the apoplastic surface of PpCESA5. Mutating any one of 18 of these amino acid residues to alanine, thereby removing their side chains, abolished or impaired CESA function, with the strongest effects observed upon the loss of charged amino acid side chains. This provides direct evidence to support the hypothesis that multiple amino acid residues collectively maintain a smooth energy landscape within the TM channel to facilitate glucan translocation.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2017

Integrating biomass quality variability in stochastic supply chain modeling and optimization for large-scale biofuel production

The production of biofuels using second-generation feedstocks has been recognized as an important alternative source of sustainable energy and its demand is expected to increase due to regulations such as the Renewable Fuel Standard. However, the pathway to biofuel industry maturity faces unique, unaddressed challenges. Here, to address this challenges, this article presents an optimization model which quantifies and controls the impact of biomass quality variability on supply chain related decisions and technology selection. We propose a two-stage stochastic programming model and associated efficient solution procedures for solving large-scale problems to (1) better represent the random nature of the biomass quality (defined by moisture and ash contents) in supply chain modeling, and (2) assess the impact of these uncertainties on the supply chain design and planning. The proposed model is then applied to a case study in the state of Tennessee. Results show that high moisture and ash contents negatively impact the unit delivery cost since poor biomass quality requires the addition of quality control activities. Experimental results indicate that supply chain cost could increase as much as 27%–31% when biomass quality is poor. We assess the impact of the biomass quality on the topological supply chain. Our case study indicates that biomass quality impacts supply chain costs; thus, it is important to consider the impact of biomass quality in supply chain design and management decisions.

09 BIOMASS FUELS↗

DOE OSTI2021

Complex Relationship between Side-Chain Polarity, Conductivity, and Thermal Stability in Molecularly Doped Conjugated Polymers

Molecularly doped conjugated polymers with polar side chains are an emerging class of conducting materials exhibiting enhanced and thermally stable conductivity. In this work, we study the electronic conductivity (σ) and the corresponding thermal stability of two polythiophene derivatives comprising oligoethylene glycol side chains: one having oxygen attached to the thiophene ring (poly(3-(methoxyethoxyethoxy)thiophene) (P3MEET)) and the other having a methylene spacer between the oxygen and the thiophene ring (poly(3-(methoxyethoxyethoxymethyl)thiophene) (P3MEEMT)). Thin films were vapor-doped with fluorinated derivatives of tetracyanoquinodimethane (FnTCNQ, n = 4, 2, 1) to determine the role of dopant strength (electron affinity) in maximum achievable σ. Specifically, when vapor doping with F 4 TCNQ, P3MEET achieved a substantially higher σ of 37.1 ± 10.1 S/cm compared to a σ of 0.82 ± 0.06 S/cm for P3MEEMT. Structural characterization using a combination of X-ray and optical spectroscopy reveals that the higher degree of conformational order of polymer chains in the amorphous domain upon doping with F 4 TCNQ in P3MEET is a major contributing factor for the higher σ of P3MEET. Additionally, vapor-doped P3MEET exhibited superior thermal stability compared to P3MEEMT, highlighting that the presence of polar side chains alone does not ensure higher thermal stability. Molecular dynamics simulations indicate that the dopant–side-chain nonbond energy is lower in the P3MEET:F 4 TCNQ mixture, suggesting more favorable dopant–side-chain interaction, which is a factor in improving the thermal stability of a polymer/dopant pair. Our results reveal that additional factors such as polymer ionization energy and side-chain–dopant interaction should be taken into account for the design of thermally stable, highly conductive polymers.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Electronic and Magnetic Properties of Oligomers and Chains of Poly(benzodifurandione) (PBDF), A Highly Conducting n-Type Polymer

The seminal development of highly electrically conducting polyacetylene via oxidative or reductive treatment (“doping”) has continuously inspired the search for other conducting π-conjugated polymers. Recently, poly(benzodifurandione), PBDF, was reported to have unexpected solubility given the absence of side chains and to exhibit an unprecedented, high electrical conductivity upon reduction (“n-doping”), with protons acting as counterions. Here, we theoretically investigate the electronic and magnetic properties of PBDF by taking long oligomers and one-dimensional (1D) periodic chains as model systems. With the oligomer models, we characterize the formation of polarons and bipolarons in n-doped PBDF. Our results indicate that singlet bipolarons tend to be the energetically most favorable species when protons bind to two closely located carbonyl groups in nearest-neighbor benzodifurandione moieties. The calculations on the 1D periodic chain models show that the positions of the protonated carbonyl groups determine the metallic, semiconducting, or insulating nature of a PBDF chain. When the protonated carbonyl groups are all situated on the same side of a PBDF chain, a stable helical chain configuration is found that exhibits ferromagnetic behavior. Our findings elucidate the mechanism of polaron and bipolaron formation in long oligomers of n-doped PBDF and highlight the fascinating electronic and magnetic properties of periodic 1D chains. Furthermore, these studies also provide a stepping stone for investigations of PBDF thin films, for which two- and three-dimensional structures must be considered.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Transport and Morphology of a Proton Exchange Membrane Based on a Doubly Functionalized Perfluorosulfonic Imide Side Chain Perflourinated Polymer

There is a critical need for higher performing proton exchange membranes for electrochemical energy conversion devices that would enable higher temperature and drier operating conditions to be utilized. A novel approach is to utilize multiacid side chains in a perfluorinated polymer, maintaining the mechanical properties of the material, while dramatically increasing the ion-exchange capacity; however, as we show in this paper, the more complex side chain gives rise to unexpected physical phenomena in the material. In this work we have thoroughly investigated a doubly functionalized perfluorosulfonic imide acid side chain perfluorinated polymer (PFIA), the simplest of many possible multiacid side chains currently being developed. The material is compared to its simpler perfluorosulfonic acid (PFSA) analogue via a battery of characterization and modeling investigations. The doubly functional side chain profoundly influences the properties of the PFIA polymer as it gives rise to both inter- and intraside chain interactions. These affect the nature of thermal decomposition of the material but, more importantly, force the backbone of the polymer into an unusually highly ordered more crystalline configuration. Under water saturated conditions, the PFIA has the same proton conductivity as the PFSA material, indicating that the additional proton does not contribute to the ionic conductivity, but the PFIA shows higher proton conductivity at lower RH conditions owing to dynamic changes in its local molecular environment. A transition is observed between 30 and 60 °C, indicating an order/disorder transition that is not present in the PFSA analogue. The mechanism of proton transport in the PFIA is due to more delocalized protons and more flexible side chains with better-dispersed, smaller water clusters forming the hydrophilic domains than in the PFSA analogue.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Observation of a Large Magnetic Anisotropy and a Field-Induced Magnetic State in SrCo(VO 4 )(OH): A Structure with a Quasi One-Dimensional Magnetic Chain

A new member of the descloizite family, a cobalt vanadate, SrCo(VO 4 )(OH), has been synthesized as large single crystals using high-temperature and high-pressure hydrothermal methods. SrCo(VO 4 )(OH) crystallizes in the orthorhombic crystal system in space group P 2 1 2 1 2 1 with the following unit cell parameters: a = 6.0157(2) Å, b = 7.645(2) Å, c = 9.291(3) Å, V = 427.29(2) Å 3 , and Z = 4. It contains one-dimensional Co–O–Co chains of edge-sharing CoO 6 octahedra along the a -axis connected to each other via VO 4 tetrahedra along the b -axis forming a three-dimensional structure. The magnetic susceptibility of SrCo(VO 4 )(OH) indicates an antiferromagnetic transition at 10 K as well as unusually large spin orbit coupling. Single-crystal magnetic measurements in all three main crystallographic directions displayed a significant anisotropy in both temperature- and field-dependent data. Single-crystal neutron diffraction at 4 K was used to characterize the magnetically ordered state. The Co 2+ magnetic spins are arranged in a staggered configuration along the chain direction, with a canting angle that follows the tipping of the CoO 6 octahedra. The net magnetization along the chain direction, resulting in ferromagnetic coupling of the a -axis spin components in each chain, is compensated by an antiferromagnetic interaction between nearest neighbor chains. A metamagnetic transition appears in the isothermal magnetization data at 2 K along the chain direction, which seems to correspond to a co-alignment of the spin directions of the nearest neighbor chain. We propose a phenomenological spin Hamiltonian that describes the canted spin configuration of the ground state and the metamagnetic transition in SrCo(VO 4 )(OH).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Side-Chain and Ring-Size Effects on Permeability in Artificial Water Channels

Artificial water channels (AWCs) have emerged as a promising framework for stable water permeation, with water transport rates comparable to aquaporins (3.4–40.3 × 10 8 H 2 O/channel/s). In this study, we probe the influence of ring-size and side-chain length on the water permeability observed within a class of AWCs termed ligand-appended pillar[n]arenes (LAPs) that have an adjustable ring-size (m) and side-chain length (n). Through all-atom molecular dynamics simulations, we calculate the permeability of these channels using the collective diffusion model and find their permeabilities. We characterize the mechanistic influence of pillar[n]arene ring-size and side-chain length on the channel water permeability by analyzing the characteristics of the internal permeating water-wire and the surrounding channel structure. We observe that water permeability decreases as a function of increasing ring-size due to increases in hydrophilic contacts between the permeating water-wire and the oxygen groups on the channel wall. Further, we observe an increase in water permeability as a function of side-chain length due to increased partitioning of the channel terminal groups into the hydrophilic blocks of the surrounding bilayer. For the LAP6 channel, with increase in side-chain length, the distance between terminal groups increases and leads to an increase in pore size, thereby enhancing water permeability. In the case of LAP5, as side-chain length increases, the channel displays a compensatory effect between tilt and bend angle due to the flexible side-chains. Such flexibility leads to higher terminal group partitioning in the hydrophilic blocks of the bilayer and extends the permeating water-wire. Furthermore, this increase in water-wire length and hydrophilic block access overcomes the nonmonotonic pore size trend in pillar[5]arene channels.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Effects of Asymmetric Molecular Architecture on Chain Stretching and Dynamics in Miktoarm Star Copolymers

We use broad-band dielectric spectroscopy (BDS) and small-angle X-ray scattering (SAXS) to investigate the impact of architectural asymmetry in the miktoarm star copolymer on the dielectric polymer relaxations. The miktoarm copolymers studied contain one or two polystyrene (PS) chains of constant molecular weight and two identical poly(cis-1,4-isoprene) (PI) chains with varied molecular weights. Using the chains in the PI block as dielectric probes, we find that the architecturally asymmetric miktoarm star copolymer systems (PSPI 2 ) feature distributions in chain relaxation times and dielectric relaxation strengths that are not dependent on molecular weight or morphology, in stark contrast to the effects of morphological confinement observed for symmetric diblock systems (PS-b-PI or PS 2 PI 2 ). Along with evidence from the SAXS measurements regarding phase separation, these results are attributed to influences from chain stretching within the framework of the Gaussian chain model for block copolymer systems. As such, the molecular architecture in block copolymers happens to be a versatile handle to control polymer chain dynamics and, ultimately, the macroscopic physicochemical properties in architecturally complex polymers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Effect of Corona Block Length on the Structure and Chain Exchange Kinetics of Block Copolymer Micelles

The effect of corona block length on micelle structure and molecular chain exchange kinetics has been investigated for a series of dilute poly(styrene)-b-poly(ethylene-alt-propylene) (SEP) diblock copolymer micelles with constant PS core block length ($\langle$N core $\rangle$ ≈ 255) but different PEP corona block lengths (($\langle$N corona $\rangle$ = 256–2080), using a combination of dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and time-resolved small-angle neutron scattering (TR-SANS). Smaller core radii and aggregation numbers, but significantly thicker corona layers (proportional to N corona 0.7 ), were observed with increasing corona block length. Furthermore, 2 orders of magnitude more rapid chain exchange was observed in SEP micelles with the longest corona block compared to the shortest. This effect is attributed to the entropic gain arising from the relief of corona chain stretching upon chain expulsion. We further extend a previous theoretical model by explicitly including a corona term associated with the entropy change in the chain exchange process, which successfully explains the influence of the corona blocks on chain exchange. Our results are in excellent agreement with simulation results of Li and Dormidontova but are apparently contradictory with Halperin and Alexander’s theory for hairy micelles and with experimental observations in two other systems that the exchange kinetics slow down with increasing corona block length. These discrepancies reveal unanticipated complexity regarding the role of the corona block in chain exchange.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

How Does the Rate of Chain Exchange Relate to Stress Relaxation in Triblock Copolymer Networks?

The relationship between macroscopic stress relaxation and molecular-level chain exchange in triblock copolymer micelles has been explored using rheology and time-resolved small-angle neutron scattering (TR-SANS), marking the first measurements of chain exchange in concentrated triblock networks. It has long been assumed in models of transient or thermoreversible networks that the time scales for these two processes are equal. Experimentally, we find that stress relaxation occurs many orders-of-magnitude faster than chain exchange. This difference is quantitatively explained by modest dispersity in the core block that results in a slight asymmetry within any given nominally symmetric triblock. For stress relaxation to occur, only the shorter chain must pull out, while chain exchange is slowed due to the requirement of the eventual pullout of the longer block. The pullout time is extremely sensitive to the length of the core block. This mechanism is supported by measurements with an intentionally asymmetric triblock copolymer, which displays an even larger difference between the stress relaxation and chain exchange rates. These results establish a quantitative molecular-level picture of the chain dynamics associated with stress relaxation in triblock copolymer networks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Self-Organization of Triblock Copolymer Melt Chains Physisorbed on Non-neutral Surfaces

In this study, we report the self-organization process of poly(styrene- b -ethylene/butadiene- b -styrene) (SEBS) triblock copolymer chains physically adsorbed on a non-neutral surface. Spin-cast SEBS thin films were prepared on silicon (Si) substrates and then annealed at a high temperature far above the bulk glass transition temperatures of the two constituent blocks. To reveal the buried interfacial structure, we utilized solvent rinsing processes and a suite of surface-sensitive techniques including ellipsometry, X-ray reflectivity, atomic force microscopy, and grazing incidence small angle X-ray scattering. We revealed that the SEBS chains form two different chain structures on the substrate simultaneously: (i) “flattened chains” with the average height of 2.5 nm but without forming microdomain structures; (ii) “loosely adsorbed chains” with the average height of 11.0 nm and the formation of perpendicularly oriented cylindrical microdomains to the substrate surface. In addition, the kinetics to form the perpendicular-oriented cylinder was sluggish (~200 h) and proceeded via multistep processes toward the equilibrium state. We also found that the lateral microdomain structures were distorted, and the characteristic lengths of the microdomains were slightly different from the bulk even after reaching “quasiequilibrium” state within the observed time window. Furthermore, we highlight the vital role of the adsorbed chains in the self-assembling process of the entire SEBS thin film: a long-range perturbation associated with the adsorbed chains propagates into the film interior, overwhelming the free surface effect associated with surface segregation of the lower surface tension of polystyrene blocks.

36 MATERIALS SCIENCE↗