Effect of Low-temperature Imidization on Properties and Aggregation Structures of Polyimide Films with Different Rigidity

The traditional high-temperature preparation process of polyimide can cause many problems and limits the wider application in extreme conditions.An important challenge to be solved urgently is the reduction of imidization temperature.In this work,twelve kinds of polyimide films with different chain rigidity were prepared at low temperature of 200℃,in the absence or presence of imidazole used as the catalyst.The molecular rigidity and free volume were theoretically calculated,and relationship between structure and properties were systematically studied.The results show that imidization reaction under low temperatures is significantly affected by the rigidity of molecula r chains.The rigid structure of polyimide is not conducive to the low-temperature imidization,but this adverse effect can be eliminated by adding catalyst,resulting the notably increased imidization degree.The optical and thermal properties can be improved to a certain extent for the chemically catalyzed system,resulting in relatively higher heat resistance and thermal stability.While the mechanical performance could be determined by com plicating factors,greatly different from polyimide films prepa red by high temperature method.To investigate aggregation structures of film s,the effect of chain rigidity and catalyst on the stacking or orientation of molecular chains was further elaborated.This wo rk can contribute to the understanding of chemically catalyzed imidization that is rarely reported in the existing research,and will provide guidance for the low-temperature preparation of high-performance polyimides.

Effect of Aggregation Structure on Thermal Expansion Behavior of Polyimide Films with Different Thickness

Polyimide films derived from representative PMDA/ODA were prepared with thickness ranging from 5 μm to 25 μm,and the effect of aggregation structure on thermal expansion behavior along different directions was studied.Both in-plane and out-of-plane linear thermal expansion(CTEand CTE) were respectively characterized by thermal mechanical analysis and FT-near-IR interference method.Volumetric and anisotropic behavior of thermal expan sion were also investigated.With increasing film thickness,CTEgradually increased from 32.2 ppm/℃ to46.1 ppm/℃ while CTEdecreased from 149.7 ppm/℃ to 128.2 ppm/℃.Volumetric thermal expansion of polyimide films was less sensitive to the va ried thickness,but anisotropy of thermal expansion was reduced.Polyimide film of 5 μm thickness showed large birefringence,indicating more considerable in-plane chain orientation anisotropy.Besides,molecular chains were more densely packed along in-plane direction when film thickness increased,while became loosely stacked in the out-of-plane direction.In contrast to the enhanced lateral chain packing for thicker film s,higher vertical chain packing order was found in thinner films.The variation of aggregation structure during thermal expansion procedure was analyzed by temperature-dependent WAXD.It is proved that thermal expansion behavior of thinner films could be largely attributed to molecular chain packing,whereas that may be influenced by many factors for thicker films in addition to the effect of chain packing.The results revealed that thermal expansion of films with thickness variation is closely related to molecular chain orientation and packing,which is associated with both chemistry and morphological structure of polyimide.

Tuning the aggregation structure and electrical property of 2.6-diphenyl-anthracene by the density of octadecyltrichlorosilane

The physical and chemical properties of organic semiconductors are closely related to their aggregation structure. Tuning of aggregation structure and electrical property is important for the application in organic electronics. In this study, a facile way to tune the aggregation structure and electrical property of 2.6-diphenyl-anthracene(DPA) is realized by using the octadecyltrichlorosilane(OTS) modification layer with different density which is fabricated by controlling reaction temperature and time.Compared with low density OTS, DPA forms larger grain size, less grain boundaries, and better molecular ordering on high density OTS surface. As a result, the charge transporting mobility of DPA film on high density OTS surface is about two orders of magnitude higher than that on low density OTS surface. The tunable aggregation structure and electrical property of DPA demonstrated here would be meaningful for the application of DPA in organic electronics.

Aggregation Behavior and Structure of Associated Polyacrylamide Hydrophobically Modified with 2-Phenoxylethylacrylate

The aggregation behavior and structure of hydrophobically modified block copolymers of acrylamide and 2-phenoxylethylacrylate were investigated by viscometry, 1H NMR relaxation, 2D NOESY, fluorescence and dynamic light scattering. It Was found that the aggregation behavior was strongly dependent on the concentration of polymer solution and the hydrophobe contents. With varying concentration from 2.0, 6.0, 8.0 to 12.0 g/L, there were different aggregate morphologies distributed in aqueous solutions, such as monopolymer chain, micelle-like aggregate, multi-micelle aggregate and cross-linked network. According to the model of aggregation, it can give a reasonable explanation on the large magnitude enhancement of viscosity with the increasing of polymer concentration. Additional data of 2D NOESY and fluorescence show that the copolymer with higher hydrophobe content（molar fraction≥ 1%） is likely to form intra-molecular association.

THE STRUCTURE OF AGGREGATION STATE AND ISOTHERMAL CRYSTALLIZATION KINETICS OF NYLON-1010

The structure of aggregation state and isothermal crystallization behavior of Nylon-1010 have been studied by WAXD, DSE, Variance-Range Function and density measurement. The results show that crystallization of Nylon-1010 has the most suitable annealing temperature, the crystals of the Nxlon-1010 are two-dimension heterogeneous nucleation. Both low treatment temperature and high crystallization te, temperature are disadvantageous for Nylon-1010 crystal growth.

AGGREGATE STRUCTURE OF FINE POWDER AND COMPACTION PROCESS

Compacting process of fine powder is greatly affected by the aggregate structure of particles. According to the experiment in which several kinds of silicon nitrides in different partical shape and size were compacted in uniaxialorientation, it is found that the volume compacting rate offorming body differs with the pressure. The aggregatestructure of each sample A, B or C was estimated by applying Cooper's equation to the analysis of the compacting process of each sample

Effect of Fluorination on Aggregate Structure of Perylene Diimide

The effect of fluorination on the aggregate structure of a novel fluorinated perylene diimide, N, N'-diperfluorophenyl-3, 4, 9, 10-perylenetetracarboxylic diimide 1, was investigated by UV-Vis absorptions and the conformation simulations from AM1 semi-empirical quantum mechanics modeling. The results showed that in the solid film 1 molecules stacked with the perfluorinated phenyl groups straightly over or below the perylene cores of the adjacent 1 molecules.

A Method for Directly Counting and Quantitatively Comparing Aggregated Structures during Cluster Formation

Assembling of a few particles into a cluster commonly occurs in many systems.However,it is still challenging to precisely control particle assembling,due to the various amorphous structures induced by thermal fluctuations during cluster formation.Although these structures may have very different degrees of aggregation,a quantitative method is lacking to describe them,and how these structures evolve remains unclear.Therefore a significant step towards precise control of particle self-assembly is to describe and analyze various aggregation structures during cluster formation quantitatively.In this work,we are motivated to propose a method to directly count and quantitatively compare different aggregated structures.We also present several case studies to evaluate how the aggregated structures during cluster formation are affected by external controlling factors,e.g.,different interaction ranges,interaction strengths,or anisotropy of attraction.

THE INFLUENCE OF HEAT TREATMENT ON STRUCTURES OF THE AGGREGATED STATE OF POLYAMIDE-1010

The structural parameters of the aggregated state of polyamide (PA)-1010 annealed at various temperatures were computed by means of the desmearing intensity from Smalt Angle X-ray Scattering (SAXS) measurements and by using the concept of the distance distribution function. The results indicated that the structural parameters of the aggregated state were strongly dependent upon heat treatment conditions and the maximum values of the structural parameters were obtained for the samples annealed at T = 175 degrees C. The particle size Z annealed at different temperature was ranged between 8.1-12.8nm, and the values of the distance distribution function P-max(Z) were obtained when Z = 4.0-6.8 nm. Using one dimension electron density correlation function (1D EDCF) method long period (L) and thickness of the lamellar (d(0)) were estimated and were found to increase with the increase of the degree of crystallinity.

Control over the aggregated structure of donor–acceptor conjugated polymerfilms for high-mobility organicfield-effect transistors

Donor–acceptor(D-A)conjugated polymers have demonstrated great potential in organicfield-effect transistors application,and their aggregated structure is a crucial factor for high charge mobility.However,the aggregated structure of D-A conjugated polymerfilms is complex and the structure–property relationship is difficult to understand.This review provides an overview of recent progress in controlling the aggregated structure of D-A conjugated polymerfilms for higher mobility,including the mechanisms,methods,and properties.Wefirst discuss the multilevel microstructures of D-A conjugated polymerfilms,and then summarize the current understanding of the relationship betweenfilm microstructures and charge transport properties.Subsequently,we review the theory of D-A conjugated polymer crystallization.After that,we summarize the common methods to control the aggregated structure of semi-crystalline and near-amorphous D-A conjugated polymerfilms,such as crystallites and aggregates,tie chains,film alignment,and attempt to understand them from the basic theory of polymer crystallization.Finally,we provide the current challenges in controlling the aggregated structure of D-A conjugated polymerfilms and in understanding the structure–property relationship.

A Study on the Impact of Chemical Structure on the Evolution of Aggregate Structure in Fiber-shaped High Density Polyethylene Vitrimer

Vitrimers have emerged as a prominent research area in the field of polymer materials.Most of the studies have focused on synthesizing polymers with versatile dynamic crosslinking structures,while the impact of chemical structure on aggregate structure of vitrimers,particularly during polymer processing,remains insufficiently investigated.The present study employed commercial maleic anhydride-grafted-high density polyethylene(M-g-HDPE)as the matrix and hexanediol as the crosslinker to facilely obtain fiber-shaped HDPE vitrimers through a reaction extrusion and post-drawing process.Through chemical structure characterization,morphology observation,thermal and mechanical properties investigation,as well as aggregate structure analysis,this work revealed the influence of dynamic bonds on the formation of aggregate structures during fiber-shaped vitrimers processing.A small amount of dynamic bonds in HDPE restricts the motion of PE chain during melt-extruding and post-drawing,resulting in a lower orientation of the PE chains.However,lamellar growth and fibril formation during post-drawing at high temperature are enhanced to some extent due to the competition between dynamic bond and chain relaxation.The uneven morphology of fibershaped HDPE vitrimers can be attributed to the stronger elastic effect brought by dynamic bonding,which plays a more dominant role in determining the mechanical properties of fiber-shaped vitrimers compared to aggregate structure.Abstract Vitrimers have emerged as a prominent research area in the field of polymer materials.Most of the studies have focused on synthesizing polymers with versatile dynamic crosslinking structures,while the impact of chemical structure on aggregate structure of vitrimers,particularly during polymer processing,remains insufficiently investigated.The present study employed commercial maleic anhydride-grafted-high density polyethylene(M-g-HDPE)as the matrix and hexanediol as the crosslinker to facilely obtain fiber-shaped HDPE vitrimers through a reaction extrusion and post-drawing process.Through chemical structure characterization,morphology observation,thermal and mechanical properties investigation,as well as aggregate structure analysis,this work revealed the influence of dynamic bonds on the formation of aggregate structures during fiber-shaped vitrimers processing.A small amount of dynamic bonds in HDPE restricts the motion of PE chain during melt-extruding and post-drawing,resulting in a lower orientation of the PE chains.However,lamellar growth and fibril formation during post-drawing at high temperature are enhanced to some extent due to the competition between dynamic bond and chain relaxation.The uneven morphology of fibershaped HDPE vitrimers can be attributed to the stronger elastic effect brought by dynamic bonding,which plays a more dominant role in determining the mechanical properties of fiber-shaped vitrimers compared to aggregate structure.

STUDIES ON SELF-ASSOCIATIVE BEHAVIOR OF A NOVEL CATION AMPHIPHILIC POLYMER

A novel associating polymer P(AEBA) was synthesized by radical polymerization of the cationic amphiphilic monomer,4-(2-(acryloyloxy)ethoxy)benzyl tri-ethyl ammonium bromide(AEBA),in aqueous solutions.P(AEBA) displays a strong tendency for self-association in aqueous solutions and is sensitive to the external stimulation such as added salt.The associative properties and morphologies of P(AEBA) were studied by fluorescnece probe technique,viscometry and TEM.In dilute salt-free solutions P(AEBA) behaves as pol...

Aging Characteristics of XLPE Insulation of 110 kV Cables in the Initial Stage of Operation

The aging characteristics of the XLPE insulation of 110 kV power cables in the initial stage of operation are studied in this paper.The XLPE insulation from cables with different running time was tested by using electrical and physicochemical methods,from which the degradation state of XLPE under multiple stresses during operation was derived.The broadband dielectric spectrum test taken from 10–1 to 10^(6) Hz showed that the dielectric constant and dielectric loss of the XLPE insulation first decrease and then increase with the increase of cable running time,which show obvious variation until 10 years of operation.The AC breakdown strengths of the XLPE insulation of operated cables with the service year no longer than 10 years were higher than that of new cables.The mechanical properties of the XLPE insulation showed no dependence with the cable running time.The crystallinity and perfection of the crystallization area were found to be enhanced during operation and the polar functional groups inside the XLPE insulation were found to be determined not only by the cross-linking by-products but also by the oxidation process during cable operation.The experimental results in this paper are important for improving the operation reliability and reducing the maintenance costs of the cables.

HYDROPHOBICALLY ASSOCIATING POLYACRYLAMIDES MODIFIED BY A NOVEL SELF-ASSOCIATIVE CATIONIC MONOMER

A series of hydrophobically associating polyacrylamides modified by small amounts （〈 3 mol%） of a self- associative cationic monomer 4-（2-（acryloyloxy） ethoxy） benzyl tri-ethyl ammonium bromide （AEBA） as hydrophobe were synthesized by radical copolymerization in aqueous solutions without external surfactants. The resulting eopolymers containing a multiblock structure exhibited a high tendency for hydrophobic association and a high thickening capacity. Solution properties and aggregation structures were investigated by viscometry and fluorescence technique. The high viscosity enhancement was found as the polymer concentration beyond a critical value c＊ and strongly depended on the copolymer microstructures. The number and length of hydrophobic microblocks within the copolymer backbones could be controlled by changing the AEBA concentration in copolymerization system. Addition of salt induced more hydrophobic association and viscosity enhancement. The synthesis method used was simple and environmentally friendly without any external surfactant contamination in comparison with the conventional micellar copolymerization.

Blue-green Phosporescent Iridium Complex with Terdentate Ligand

An ionic iridium（Ⅲ） complex[Ir（F2dpyb）（bzdpp）2Cl][OTf]with 1,3-difluoro-4,6-di（2-pyridinyl） benzene（F2dpybH） terdentate ligand and benzyldiphenylphosphine（bzdpp）ligand was synthesized and characterized.The structure of iridium complex was verified by single-crystal X-ray crystallography.It crystallizes in monoclinic,space group P21/n with a =14.3654（7）,b = 23.0026（10）,c = 15.7964（7） A°,β = 97.6029（11）,V= 5173.9（4） A°3,Z = 4,F（000） =2552,Dc = 1.645 Mg/m^3,Mr = 1281.49 and μ = 0.071 mm^-1.The UV-vis absorption and phosphorescence of the complex were discussed.The complex was ＇aggregation induced emission（AIE）＇ active.It exhibited no emission in CH2Cl2 solution but strong blue-green emission in solid state under ultraviolet light excitation.The complex emitted a strong phosphorescence centered at493 nm when doped in PMMA.Its lifetime is 0.755 μs and quantum yield is approximately 0.134.

Application of Air-cooled Blast Furnace Slag Aggregates as Replacement of Natural Aggregates in Cement-based Materials：A Study on Water Absorption Property

The influence of air-cooled blast furnace slag aggregates as replacement of natural aggregates on the water absorption of concrete and mortar was studied, and the mechanism was analyzed. The interface between aggregate and matrix in concrete was analyzed by using a micro-hardness tester, a laser confocal microscope and a scanning electron microscope with backscattered electron image mode. The pore structure of mortar matrixes under different curing conditions was investigated by mercury intrusion porosimetry. The results showed that when natural aggregates were replaced with air-cooled blast furnace slag aggregates in mortar or concrete, the content of the capillary pore in the mortar matrix was reduced and the interfacial structure between aggregate and matrix was improved, resulting in the lower water absorption of mortar or concrete. Compared to the concrete made with crushed limestone and natural river sand, the initial absorption coefficient, the secondary absorption coefficient and the water absorption capacity through the surface for 7 d of the concrete made from crushed air-cooled blast furnace slag and air-cooled blast furnace slag sand were reduced by 48.9%, 52.8%, and 46.5%, respectively.

Halogenated Thienoacene Derivatives with Improved Emission Properties

Thienoacenes is one of most important groups of semiconducting materials due to the high stability and superior mobility.However,there are scarce studies on the emission properties of thienoacenes to date.Herein,we synthesized fluorinated and chlorinated dibenzo[d,d’]thieno[3,2-b;4,5-b’]dithiophenes(DBTDTs)derivatives F6-DBTDT and Cl6-DBTDT by sulfoxide cyclization,significantly lowering the energy levels relative to the parent compound DBTDT.According to single crystal structure analysis,F6-DBTDT molecules adopt one-dimensional slipped stacking with closeπ-πinteractions of 3.43Å(1Å=0.1 nm),which is different from the parent compound DBTDT with herringbone stacking motif.Interestingly,the halogenated DBTDT derivatives exhibit enhanced emission properties both in solution and in the solid state,opening up possiblities to improve photoluminescence of thienoacences by halogenation.

High micropore-utilization carbon aerogel with controlled nanostructures via adjusting aggregation state of polyacrylonitrile for energy storage systems

Designing and optimizing the pore structure of porous carbon electrodes is essen-tial for diverse energy storage systems.In this study,an innovative approach spray phase-inversion strategy was developed for the rapid and efficient fabri-cation of controlled porous carbon aerogel.Moreover,the aggregation structure of polyacrylonitrile is controlled by adjusting the Hansen’s solubility parameter,thereby regulating the electrode material structure.Furthermore,the theoretical analysis of the spray phase-inversion process revealed that this regulation pro-cess is jointly regulated by solvent hydrodynamic diameter and phase-inversion kinetics.Through optimization,a novel porous carbon material was obtained that exhibited excellent performance as an electrode material.When utilized in supercapacitors for energy storage,it demonstrated a high specific capacitance of 373.1 F g^(-1) in a 6 M KOH electrolyte solution.Simultaneously,it has been observed that the preparation strategy for porous electrodes offers notable advan-tages in terms of excellent designability,broad universality,simplicity,and high efficiency,thereby holding promise for large-scale fabrication of diverse porous electrode materials and various types of electrodes for diverse energy storage applications.

Control of aggregated structure of photovoltaic polymers for high-efficiency solar cells

π-Conjugated organic/polymer materials-based solar cells have attracted tremendous research interest in the fields of chemistry,physics,materials science,and energy science.To date,the best-performance polymer solar cells(PSCs)have achieved power conversion efficiencies exceeding 18%,mostly driven by the molecular design and device structure optimization of the photovoltaic materials.This review article provides a comprehensive overview of the key advances and current status in aggregated structure research of PSCs.Here,we start by providing a brief tutorial on the aggregated structure of photovoltaic polymers.The characteristic parameters at different length scales and the associated characterization techniques are overviewed.Subsequently,a variety of effective strategies to control the aggregated structure of photovoltaic polymers are discussed for polymer:fullerene solar cells and polymer:nonfullerene small molecule solar cells.Particularly,the control strategies for achieving record efficiencies in each type of PSCs are highlighted.More importantly,the in-depth structure-performance relationships are demonstrated with selected examples.Finally,future challenges and research prospects on understanding and optimizing the aggregated structure of photovoltaic polymers and their blends are provided.

Numerical study of soil-rock mixture:Generation of random aggregate structure

The soil-rock mixture(SRM) is highly heterogeneous. Before carrying out numerical analysis,a structure model should be generated. A reliable way to obtain such structure is by generating random aggregate structure based on random sequential addition(RSA). The classical RSA is neither efficient nor robust since valid positions to place new inclusions are formulated by trial, which involves repetitive overlapping tests. In this paper, the algorithm of Entrance block between block A and B(EAB)is synergized with background mesh to redesign RSA so that permissible positions to place new inclusions can be predicted,resulting in dramatic improvement in efficiency and robustness.