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SEMI-QUANTITATIVE CHARACTERIzATION OF SEGMENT dISTRIBUTION IN LLdPE BASEd ON THERMAL SEGREGATION

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Chinese Journal of Polymer Science 2002年第4期20卷 347-352页

作者： stephen z.d.cheng Maurice Morton Institute and department of Polymer Science University of Akron Akron Lhio 44325-3909 USA

Based on successive multiple-step isothermal crystallization and self-nucleation annealing methods, a novel semi-quantitative method for the characterization of segment distribution in linear low density polyethylene (LLdPE) was established by treating the thermal analysis data using the Gibbs-Thomson equation. The method was used to describe the segment distribution of ziegler-Natta catalyzed LLdPE (z-N LLdPE), metallocene catalyzed LLdPE (m-LLdPE) and two commercial LLdPEs with wide molecular weight distribution. The differences of the results obtained from the two thermally treated samples were compared. The results of segment distribution of the polymers were discussed according to their microstructure data and were compared with their characteristics. It can be deduced from the results that this characterization method is effective to characterize the sequence structure of the branched ethylene copolymers.

关键词： characterization segment distribution linear low density polyethylene thermal segregation

Spherical Packing Superlattices in Self-Assembly of Homogenous Soft Matter:Progresses and Potentials

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Chinese Journal of Polymer Science 2023年第5期41卷 607-620,I0005页

作者： Yuchu Liu Huanyu Lei Qing-Yun Guo Xianyou Liu Xinghan Li Yuean Wu Weiyi Li Wei zhang Geng Xin Liu Xiao-Yun Yan stephen z.d.cheng South China Advanced Institute for Soft Matter Science and Technology School of Molecular Science and EngineeringSouth China University of TechnologyGuangzhou 510640China School of Polymer Science and Polymer Engineering The University of AkronAkron OH 44325-3909USA State Key Laboratory for Modification of Chemical Fibers and Polymer Materials Center for Advanced Low-dimension MaterialsCollege of Material Science and EngineeringDonghua UniversityShanghai 201620China

The construction of complex superlattices using homogenous soft matter has great potential for the bottom-up fabrication of complex,nanoscale structures.This topic is not only interested in scientific exploring for new concepts of supramolecular crystals with nanometer in sizes,which is about thousand times larger in volumes than those of normal crystals,but also practically important to provide construction principles of metamaterials which are artificially structured materials for controlling and manipulating light,sound,and other physical behaviors.These systems have fast assembly kinetics and convenient processing procedures,making them ideal for large-scale superlattice production.In this perspective,we focus on recent developments in the construction of complex spherical packing superlattices using homogenous soft self-assemblies.We discuss the general mechanism of those formations of supramolecular motifs and provide an overview of the spherical packing superlattices self-assembled by homogenous soft matters based on different volume asymmetry.Additionally,we outline the potentials of utilizing this approach in constructing novel superlattices as well as its future challenges.

关键词： Soft matter Self-assembly Spherical packing phases Superlattice Bottom-up construction

Special topic on soft matter science and technology

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Science China Chemistry 2018年第1期61卷 1-2页

作者： Wen-Bin zhang stephen z.d.cheng Yong Cao Key Laboratory of Polymer Chemistry & Physics of Ministry of Education Center for Soft Matter Science and Engineering College of Chemistry and Molecular Engineering Peking University South China Advanced Institute of Soft Matter Science and Technology South China University of Technology State Key Laboratory of Luminescent Materials and devices South China University of Technology

Soft matter,as first proposed by de Gennes in 1991,describes a broad range of molecular systems exhibiting a large response to small foreign stimuli.Typically,it includes colloidal particles,amphiphiles,liquid crystals,polymers and others.The term"soft"originates from the common macroscopic properties of these systems and differentiates them from conventional"hard"materials.Over the past decades,the field of"soft matter"has progressed tremendously.Today,it is a truly multidisciplinary research endeavor bridging physics with chemistry and life science.

关键词： In Special topic on soft matter science and technology

TRANSIMIdIzATION IN THERMOPLASTIC POLYIMIdES

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Chinese Journal of Polymer Science 1999年第2期17卷 171-184页

作者： Yoan Kim doyun Kim Frank W.Harris stephen z.d.cheng Maurice Morton Institute and department of Polymer Science The University of Akron Akron Ohio 44325-3909 USAMaurice Morton Institute and Department of Polymer Science The University of Akron Akron Ohio 44325-3909 USAMaurice Morton Institute and Department of Polymer Science The University of Akron Akron Ohio 44325-3909 USAMaurice Morton Institute and Department of Polymer Science The University of Akron Akron Ohio 44325-3909 USA

In order to improve the processibility in thermoplastic polyimides, a new method, termed the'reactive plasticizer' approach, has been proposed. This method uses a small amount (5～15 mol%) of a lessactivated, weak nucleophilic diamine co-monomer as a 'reactive plasticizer' to obtain copolyimide resinswhich possess relatively low viscosity at low temperatures and can be readily processed through the autoclavecycle at low pressures. during a high temperature treatment, the reactive plasticizers join the reaction to formhigh molecular weight copolyimides, and the preferred material properties are thus achieved. The mosteffective reactive plasticizer is aromatic heterocyclic diamines, such as 2, 6-diaminopyridine diamine (dAP),and the transimidization involved with a reactive plasticizer has been proposed to play a major role for thesuccess of this approach. In order to understand the transimidization mechanism, three steps have been takenin this research: first, a copolyimide system of 50% of dAP and 50% 1, 4 -bis [4-aminophenoxy] benzenediamine (dOdA) with 100% of 2, 2'-bis[4-(3, 4-dicarboxyphenoxy)phenyl] propane dianhydride (Ultem^(R)dA) is prepared. Second, several specifically designed polyimide mixture systems were used, and they consistof two homopolyimides: one is Ultem^(R) dA-dOdA, and the other is Ultem^(R) dA-dAP. The third step is toinvestigate two mixture systems in which Ultem^(R) dA-dOdA is mixed with dAP monomer solution andUltem^(R) dA-dAP is mixed with dOdA monomer solution. For all systems, with increasing degree oftransimidization upon heat-treatment, the chain structures of the mixtures and their thermal and dynamicmechanical transition behaviors are investigated via one-dimensional and two-dimensional nuclear magneticresonance, differential scanning calorimetry, and dynamic mechanical analysis experiments. Experimentalresults indicate that in the mixture of two homopolyimides, transimidization takes place much moreefficiently in solution than in the melt. For the two mixtures with monomer soluti

关键词： Transmidization Thermoplastic polyimides

Frank-Kasper and related quasicrystal spherical phases in macromolecules

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Science China Chemistry 2018年第1期61卷 33-45页

作者： Mingjun Huang Kan Yue Jing Wang Chih-Hao Hsu Linge Wang stephen z.d.cheng department of Polymer Science The University of Akron South China Advanced Institute for Soft Matter Science and Technology South China University of Technology State Key Laboratory of Luminescent Materials and devices School of Materials Science and Engineering South China University of Technology

Creation of diverse ordered nanostructures via self-assembly of macromolecules is a promising "bottom-up" approach towards next-generation nanofabrication technologies. It is therefore of critical importance to explore the possibilities to form new self-assembled phases in soft matter systems. In this review, we summarized recent advances on the identification of several unconventional spherical phases in the self-assembly of functional macromolecules, including Frank-Kasper(F-K) phases and quasicrystals originally observed in metal alloys. We believe that these results provide a new strategy towards the rational design of novel functional materials with hierarchically ordered structures.

关键词： self-assembly Frank-Kasper phase quasicrystal giant surfactant block copolymer dendrimer

MOLECULAR ANd SUPRAMOLECULAR ORdERING IN CONFINEd ENVIRONMENTS

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Chinese Journal of Polymer Science 2000年第4期18卷 287-300页

作者： stephen z.d.cheng Bret H.Calhoun Roderic P.Quirk Benjamin S.Hsiao Maurice Morton Institute and department of Polymer Science The University of Akron Akron Ohio 44325-3909 USAMaurice Morton Institute and Department of Polymer Science The University of Akron Akron Ohio 44325-3909 USAMaurice Morton Institute and Department of Polymer Science The University of Akron Akron Ohio 44325-3909 USADepartment of ChemistryThe State University of New York at Stony Brook Stony Brook New York 11794-3400 USA

Crystal and phase morphologies and structures determined by self-organization of crystalline-amorphous diblockcopolymers, crystallization of the crystallizable blocks, and vitrification of the amorphous blocks are reviewed through asystematic study on a series of poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymers. On the base ofcompetitions among these three processes, molecular and supramolecular ordering in confined environments can beinvestigated. In a concentration-fluctuation-induced disordered (d_(CF)) diblock copolymer, the competition between crystalli-zation of the PEO blocks and vitrification of the PS blocks is momtored by time-resolved simultaneous small angle X-rayscattering (SAXS) and wide angle X-ray diffraction (WAXd) techniques. In the case of T_czation of thePEO blocks is observed to be confined within the bicontinuous d_(CF) phase due to the rapid vitrification of the PS-rich phase.Overall crystallization rate, crystal melting behavior, and crystallinity results further confirm the competition betweencrystallization and vitrification at different temperatures. In an ordered lamellar PEO-b-PS diblock copolymer, the crystalli-zation of the PEO blocks is completely confined within the ordered lamellae due to rapid vitrification of the PS layers asobserved by time-resolved SAXS and WAXd experiments. From the combined two-dimensional SAXS and WAXdmeasurements, the crystal orientation within the confined lamellar geometry is found parallel to the lamellar surface normalwhen it is isothermally crystallized at 35℃. In an ordered cylindrical PEO-b-PS sample, the crystallization of the PEO blocksis also observed to be confined within the ordered cylinders because of rapid vitrification of the PS matrix. The crystalorientation within the confined cylinders is found perpendicular to the cylinder axis as it is crystallized at 35℃.

关键词： Poly(ethylene oxide)-b-polystyrene diblock copolymer Molecular ordering, Supramolecular ordering, Confined environment

CHEMICALLY dEPOSITEd SILVER FILM USEd AS A SERS-ACTIVE OVER-COATING LAYER FOR POLYMER FILM

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Chinese Journal of Polymer Science 2001年第3期19卷 265-268页

作者： stephen z.d. cheng department of Polymer Science The University of Akron Akron OH 44325 USA

When colloidal silver particles were chemically deposited onto polymer film as an over-coating layer, surface-enhanced Raman scattering (SERS) spectra could be collected for the surface analysis. SERS measurements of ... 详细信息

关键词： surface enhanced Raman scattering chemically deposited silver polymer film

WHAT ARE THE dIFFERENCES OF POLYMER SURFACE RELAXATION FROM THE BULK?

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Chinese Journal of Polymer Science 2011年第1期29卷 81-86页

作者： Ian Mann Ryan M.Van Horn Jason J.Ge Matthew J.Graham Frank W.Harris stephen z.d.cheng College of Polymer Science and Polymer Engineering Department of Polymer Sciencethe University of Akron

The polymer surface relaxation in thin films has been a long debating issue. We report a new method on studying surface relaxation behaviors of polymer thin films on a solid substrate. This method involved utilizing a rubbed polyimide surface with a pretilting angle in a liquid crystalline cell. due to the surface alignment, the liquid crystals were aligned along the rubbing direction. during heating the liquid crystalline cell, we continuously monitored the change of orientation of the liquid crystals. It is understood that at a temperature where the orientation of liquid crystal is lost, the surface relaxation on the glass substrate takes place to lose the polyimide surface orientation. It was found that the relaxation temperature at which the liquid crystals lose their orientation depends on the film thickness of the polyimide. A quantitative linear relationship between the relaxation temperature and reciprocal of the film thickness can be observed. Furthermore, different topologies of the rubbed and relaxed thin films were amplified using the polyethylene decoration method and observed using atomic force microscopy.

关键词： Surface relaxation Liquid crystal orientation Polyethylene decoration.

The 2024 Compendium of Physical Activities and its expansion

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Journal of Sport and Health Science 2024年第1期13卷 1-2,F0003页

作者： stephen d.Herrmann Erik A.Willis Barbara E.Ainsworth Kansas Center for Metabolism and Obesity Research University of Kansas Medical CenterKansas CityKS 66160USA Center for Health Promotion and disease Prevention University of North Carolina at Chapel HillChapel HillNC 27599USA School of Exercise and Health Shanghai University of SportShanghai 200438China

First developed 30 years ago,the Compendium of Physical Activities(Compendium)was created to provide a standardized way of measuring and classifying specific physical activities(PAs),allowing researchers and health professionals to assess the energy expenditure and health benefits associated with different PA.1Since its inception,the Compendium has been widely utilized and recognized as a fundamental PA and health resource.

关键词： has utilized classify