Article
Chemistry, Physical
Zhong Zeng, Ziyun Li, Qili Li, Guangjie Song, Meng Huo
Summary: Polymerization-induced self-assembly (PISA) has been employed as a general strategy to fabricate biomimetic hydrogels and organogels with tailored nanostructures and excellent mechanical properties. The hydrogels with nanostructured spherical domains exhibit remarkable strength, toughness, stretchability, and recoverability, which are attributed to the unique network architecture. The successful fabrication of various nanostructured gels confirms the general feasibility of the PISA strategy and inspires the design of functional nanostructured gels.
Article
Engineering, Biomedical
Maria Leticia Bravi Costantino, Maria Soledad Belluzo, Tamara G. Oberti, Ana M. Cortizo, Maria Susana Cortizo
Summary: The present study introduces a novel copolymer synthesis and its application in membrane design, showcasing the efficient interaction with chitosan through cross-linking for potential biomedical applications. The obtained terpolymer, combined with a natural polymer, presents an interesting strategy to obtain a biomaterial with possible applications in regenerative medicine.
JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A
(2021)
Article
Polymer Science
Suna Azhdari, Fabian Herrmann, Deniz Coban, Juergen Linders, Andre H. Groeschel
Summary: This study investigates the behavior of Janus nanoparticles (JNPs) in spherical confinement and compares it to the confinement self-assembly of block copolymers. The research finds that the ordered structure of nanoparticles diminishes when the Janus balance deviates from parity.
MACROMOLECULAR RAPID COMMUNICATIONS
(2022)
Article
Polymer Science
Hui Li, Yuan-Yuan Wei, Zhen-Yu Wang, Ning Wang, Long Zhang, Zhen-Bin Chen, Qiao-Li Lin, Hong Liu
Summary: The self-assembly morphology of triblock copolymers confined between the slits of neutral plates is investigated, revealing that different types of copolymers form porous membrane structures with specific structures and pore distributions at different concentrations.
POLYMER INTERNATIONAL
(2022)
Article
Polymer Science
Eman Ahmed, C. Tyler Womble, Jinwon Cho, Kristen Dancel-Manning, William J. Rice, Seung Soon Jang, Marcus Weck
Summary: Compartmetalized micelles are prepared through self-assembly of linear triblock terpolymers with control over block sequence and distribution, offering a facile approach for target material synthesis. Various morphologies such as core-shell-corona, disk-like, raspberry-like and worm-like are observed using cryogenic transmission electron microscopy and dissipative particle dynamics simulations.
Article
Polymer Science
Manuel Troemer, Elias M. Zirdehi, Arash Nikoubashman, Andre H. Groeschel
Summary: The effect of block-selective surfactants on the confined assembly of a triblock terpolymer SBM was analyzed. It was found that different surfactants led to different morphologies and structures of the assembled microparticles. This study provides important insights into the microphase separation of block copolymers under confinement.
MACROMOLECULAR RAPID COMMUNICATIONS
(2023)
Article
Chemistry, Multidisciplinary
Cheng Zhou, Yan Chen, Mingjun Huang, Yi Ling, Liming Yang, Guochen Zhao, Jie Chen
Summary: The dual temperature-responsive triblock polymer exhibits dual thermal response behavior in water, with a UCST temperature around 20 degrees C and a LCST temperature around 31 degrees C. Properly designing the length of the blocks allows the copolymer to undergo phase transitions within the desired temperature range. The self-assembled structures of the polymer vary at different temperatures, allowing for reversible gel behavior and the possibility of dissolving different compounds in water simply by changing the temperature.
NEW JOURNAL OF CHEMISTRY
(2021)
Article
Polymer Science
Hyeongkeon Yoon, Seonghyeon Ahn, Qingshu Dong, Chungryong Choi, Eunyoung Kim, Weihua Li, Jin Kon Kim
Summary: This study investigated the formation of a multidomain double-stranded helical nanostructure, paving the way for the creation of multifunctional helical structures for various applications such as metamaterials. The experimentally observed morphology matched well with the prediction by self-consistent field theory.
Article
Polymer Science
Yuta Miyamori, Jiro Suzuki, Yoshitaka Aoyama, Tomohiro Mihira, Yushu Matsushita, Atsushi Takano
Summary: Hexagonally packed coaxial triply helical domains with mesoscopic length scale were successfully created in matrices from a blend system of S1IS2P tetrablock terpolymer/Sh homopolymer, where the intermediate S phase was found to have a helical nature due to S-2 chains filling the gap between the I and P helices. The grains composed of hexagonally packed helices exhibited homochirality.
Article
Polymer Science
Jordan T. Lovegrove, Ben A. Humphreys, Chin Ken Wong, Liliana de Campo, Anna Wang, Christopher J. Garvey, Martina H. Stenzel
Summary: This article investigates a synthetic pathway to produce biologically compatible, crosslinked, multicompartment worms (MCWs) in aqueous solution by incorporating thermoresponsive poly-N-isopropylacrylamide (PNIPAM) to direct assembly above the lower critical solution temperature (LCST). The self-assembly process and mechanism of MCWs starting from primary micelles were observed and controlled by adjusting the temperature.
Article
Chemistry, Multidisciplinary
Hongjun Jin, Ziyan Wu, Weilin Lin, Yinye Chen, Jingran Zhang, Ruyi Zheng, Haibing Wei, Qinghua Chen, Qingrong Qian, Jianbin Huang, Jie Zhang, Yun Yan
Summary: In this study, size-controllable tetragonal nanoprisms were formed through crystallization-directed ionic self-assembly (CDISA) by evaporating a micellar solution on solid substrates. The length and width of the nanoprisms can be easily tuned by varying the initial concentration. This precise size-control strategy is expected to provide new possibilities for designing advanced materials with size-controllable anisotropic nanostructures.
Article
Engineering, Chemical
Qingwu Long, Shuaifei Zhao, Jiexin Chen, Zhe Zhang, Guangxian Qi, Zhao-Qing Liu
Summary: In this study, high-performance MXene membranes with stable and tunable nanochannels were prepared by self-assembly, allowing for precise control of internal nanochannels and surface properties, resulting in excellent water permeability and molecular separation performance.
JOURNAL OF MEMBRANE SCIENCE
(2021)
Article
Chemistry, Physical
Si Shen, Ning Wang, Jing Jia, Di Song, Tingting Zuo, Ke Liu, Quantong Che
Summary: Anion exchange membranes (AEMs) with layered structures were constructed by combining layer-by-layer self-assembly membranes and electrospun nanofiber membranes. The layered structure facilitated hydroxide ions conduction and the external nanofiber membranes enhanced the chemical stability and mechanical properties of AEMs.
JOURNAL OF MOLECULAR LIQUIDS
(2022)
Article
Polymer Science
Sany Chea, Kristin Schade, Stefan Reinicke, Regina Bleul, Ruben R. Rosencrantz
Summary: The base pairing and melting behavior of oligonucleotides can be utilized to develop smart thermoresponsive and programmable materials. In this study, complementary cytidine (C) and guanosine (G) monomers were blockcopolymerized using RAFT polymerization technique with hydrophilic macro chain transfer agent. The hydrogen bond interactions between C-C, G-G, and C-G were investigated, and the self-assembly of these bioinspired compounds showed potential for future drug delivery systems.
Article
Chemistry, Multidisciplinary
Anirban Som, Alessandra Griffo, Indranath Chakraborty, Hendrik Haehl, Biswajit Mondal, Amrita Chakraborty, Karin Jacobs, Paivi Laaksonen, Olli Ikkala, Thalappil Pradeep, Nonappa
Summary: 2D nanomaterials possess a range of mechanical, electrical, optical, and catalytic properties. The self-assembly of atomically precise noble nanoclusters offers a modular approach for the synthesis of new generation 2D materials. This study demonstrates the self-assembly of silver nanoclusters into large-area membranes with strong and elastic properties. These membranes can be easily transferred to different substrates and enable the detection of antibiotic molecules without substrate pretreatment.
Article
Chemistry, Multidisciplinary
Sonal Bhadauriya, Xiaoteng Wang, Asritha Nallapaneni, Ali Masud, Zongyu Wang, Jaejun Lee, Michael R. Bockstaller, Abdullah M. Al-Enizi, Charles H. Camp, Christopher M. Stafford, Jack F. Douglas, Alamgir Karim
Summary: The concentration of nanoparticles in PNC films was found to be proportional to the thermal stability of the films, with a change in slope at a compensation temperature. Entropy-enthalpy compensation is confirmed as a general feature of PNC films, impacting the stability.
Article
Chemistry, Multidisciplinary
Wenjie Wu, Maninderjeet Singh, Ali Masud, Xiaoteng Wang, Asritha Nallapaneni, Zihan Xiao, Yue Zhai, Zongyu Wang, Tanguy Terlier, Markus Bleuel, Guangcui Yuan, Sushil K. Satija, Jack F. Douglas, Krzysztof Matyjaszewski, Michael R. Bockstaller, Alamgir Karim
Summary: The phase separation of binary mixtures of polymer-grafted nanoparticles (PGNPs) with a soft polymer-grafted layer on the inorganic core exhibits different kinetics from conventional polymer blends, and can be controlled by switching the solvent composition. Despite a relatively low coarsening exponent, the phase separation process is completed within minutes and the roughness of the blend film saturates at a scale proportional to the phase separation pattern scale. The direct immersion annealing method provides a significant opportunity for controlling the phase separation morphology of PGNP blends by solution processing.
Article
Polymer Science
Leo Gury, Samruddhi Kamble, Daniele Parisi, Jianan Zhang, Jaejun Lee, Ayesha Abdullah, Krzysztof Matyjaszewski, Michael R. Bockstaller, Dimitris Vlassopoulos, George Fytas
Summary: The study reveals that the architecture of polymer brushes significantly affects particle interactions in solution, which is crucial for the development of functional materials based on self-assembled polymer-grafted nanoparticles. The interaction potential of grafted particles is influenced by grafting density and degree of polymerization, showing different behaviors under different conditions. These findings suggest the importance of steric crowding in dense GNP systems and highlight the potential to tailor physical properties of hybrid materials by adjusting geometry rather than chemical composition.
Editorial Material
Polymer Science
Michael R. Bockstaller, Jean-Francois Lutz
PROGRESS IN POLYMER SCIENCE
(2022)
Article
Nanoscience & Nanotechnology
Maninderjeet Singh, Aman Agrawal, Wenjie Wu, Ali Masud, Edward Armijo, Damian Gonzalez, Shenghui Zhou, Tanguy Terlier, Chenhui Zhu, Joseph Strzalka, Krzysztof Matyjaszewski, Michael Bockstaller, Jack F. Douglas, Alamgir Karim
Summary: The template-free unidirectional alignment of lamellar block copolymers (l-BCPs) is important for sub-10 nm high-resolution patterning and hybrid multicomponent nanostructures. This study demonstrates a modified soft-shear-directed self-assembly approach for aligning pristine l-BCPs and l-BCPs with incorporated polymer-grafted nanoparticles (PGNPs), as well as the conversion of l-BCPs to aligned gold nanowires and hybrid line-dot nanostructures. The aligned BCPs and nanowires have potential use in nanopatterning applications, and the line-dot nanostructures could be useful in sensing biomolecules based on the plasmonic response of the nanowires.
ACS APPLIED MATERIALS & INTERFACES
(2022)
Article
Polymer Science
Yuqi Zhao, Zongyu Wang, Chenxi Yu, Hanshu Wu, Mateusz Olszewski, Rongguan Yin, Yue Zhai, Tong Liu, Amy Coronado, Krzysztof Matyjaszewski, Michael R. Bockstaller
Summary: A synthetic route for silica brush particles with random and gradient copolymer grafts was developed using SI-ATRP. The structure and thermomechanical properties of copolymer-tethered brush particle films were compared to linear copolymer analogues. Random copolymer brush systems showed uniform and narrow glass transitions, while gradient brush materials displayed a splitting of the glass-transition temperature, an increase in Young's modulus, and a decrease in ductility. The microstructure of gradient brush systems was found to be heterogeneous, while random brush and linear copolymer systems had a molecularly uniform microstructure. The results highlight the importance of geometric constraints on the physical properties of copolymer brush particle-based hybrid materials.
Article
Nanoscience & Nanotechnology
Wenjie Wu, Maninderjeet Singh, Yue Zhai, Ali Masud, Wafa Tonny, Chuqing Yuan, Rongguan Yin, Abdullah M. Al-Enizi, Michael R. Bockstaller, Krzysztof Matyjaszewski, Jack F. Douglas, Alamgir Karim
Summary: In this study, a novel solvent vapor annealing soft lithography (SVA-SL) method was developed to overcome the technical difficulties in processing high molecular-mass PGNP blends. The SVA-SL method allows for easy imprint patterning and large-scale organization of PGNPs, even with highly entangled grafted chains, resulting in enhanced thermo-mechanical properties and a wider range of potential nanotech applications.
ACS APPLIED MATERIALS & INTERFACES
(2022)
Article
Polymer Science
Rongguan Yin, Yuqi Zhao, Adam Gorczynski, Grzegorz Szczepaniak, Mingkang Sun, Liye Fu, Khidong Kim, Hanshu Wu, Michael R. Bockstaller, Krzysztof Matyjaszewski
Summary: An alternating P-(MMA/BA) copolymer was synthesized using the ARGET ATRP method, and subsequent postpolymerization modifications were performed. The modified copolymer showed different architecture compared to gradient and statistical copolymers, with a narrower range of glass transition.
Review
Chemistry, Physical
Dhriti Nepal, Saewon Kang, Katarina M. Adstedt, Krishan Kanhaiya, Michael R. Bockstaller, L. Catherine Brinson, Markus J. Buehler, Peter Coveney, Kaushik Dayal, Jaafar A. El-Awady, Luke C. Henderson, David L. Kaplan, Sinan Keten, Nicholas A. Kotov, George C. Schatz, Silvia Vignolini, Fritz Vollrath, Yusu Wang, Boris Yakobson, Vladimir V. Tsukruk, Hendrik Heinz
Summary: This Review discusses recent advancements in bioinspired nanocomposite design, focusing on the role of hierarchical structuring at different length scales in creating multifunctional, lightweight, and robust structural materials. By manipulating the architecture, interphases, and confinement, dynamic and synergistic responses have been achieved. The study highlights the significance of hierarchical structures across multiple length scales for achieving multifunctionality and robustness.
Article
Polymer Science
Yuqi Zhao, Rongguan Yin, Hanshu Wu, Zongyu Wang, Yue Zhai, Khidong Kim, Changwoo Do, Krzysztof Matyjaszewski, Michael R. Bockstaller
Summary: Van der Waals-driven self-healing in copolymers with lock-and-key architecture has been achieved by synthesizing lock-and-key copolymers with prescribed sequences. The recovery behavior of copolymers with different sequences was evaluated, and copolymers with alternating and statistical sequences showed a 10-fold increase in recovery rate compared to copolymers with a gradient sequence. The results provide strategies for designing and synthesizing engineering polymers with both structural and thermal stability and the ability to recover from structural damage.
Article
Materials Science, Multidisciplinary
Jin Han, Taolei Qiu, Dan Wu, Yue Zhai, Michael R. Bockstaller, Xiaolin Zhang, Jianchao Zhao
Summary: A new process for upcycling waste-derived DMP into hyper-crosslinked porous polymer networks is presented, which can reduce the negative environmental impact associated with the fabrication and application of PPE. The resulting polymers show promising adsorption capacity for CO2 and H2, suggesting potential applications in carbon capture.
MATERIALS TODAY COMMUNICATIONS
(2023)
Article
Materials Science, Multidisciplinary
Jin Han, Quan Chen, Yiping Feng, Yupeng Shen, Dan Wu, Mingqiang Zhong, Qiaoye Zhang, Zhengping Zhao, Yue Zhai, Michael R. Bockstaller
Summary: In this study, betaine ester-functionalized epoxy resins with tunable degradation and antibacterial activity in seawater-like environments were synthesized. Chloroacetate-decorated epoxy resins were first synthesized and reacted with tertiary amine-based curing agents. The resulting betaine ester-decorated epoxy thermosets showed a yield strength exceeding 80 MPa and tunable degradation capability. Integration of cetyl chloroacetate further enhanced the betaine ester content and bactericidal performance.
ACS APPLIED POLYMER MATERIALS
(2023)
Article
Chemistry, Physical
Yuqi Zhao, Hanshu Wu, Rongguan Yin, Chenxi Yu, Krzysztof Matyjaszewski, Michael R. Bockstaller
Summary: The effect of sequence structure on the self-healing and shape-memory properties of copolymer-tethered brush particle films was investigated. It was found that statistical copolymer sequence provided the most rapid restoration of mechanical properties and an increase of the high T(g) (MMA) component improved the material's modulus while retaining self-healing ability. The reduction of flow in brush systems was attributed to slow cooperative relaxation due to the complex microstructure.
CHEMISTRY OF MATERIALS
(2023)
Article
Chemistry, Multidisciplinary
Sonal Bhadauriya, Asritha Nallapaneni, Xiaoteng Wang, Jianan Zhang, Ali Masud, Michael R. Bockstaller, Abdullah M. Al-Enizi, Christopher M. Stafford, Jack F. Douglas, Alamgir Karim
Summary: This study compares the effects of bare silica (SiO2) nanoparticles and SiO2 nanoparticles with grafted polymer layers on the decay of nanoimprinted polymer film patterns. It shows that attractive interactions between the bare nanoparticles and the polymer matrix enhance thermal resilience, while particle brushes weaken this effect. Additionally, regardless of the NP system used, there is entropy-enthalpy compensation in the relaxation time of the pattern as a function of temperature.
NANOSCALE ADVANCES
(2021)
Review
Polymer Science
Rongguan Yin, Zongyu Wang, Michael R. Bockstaller, Krzysztof Matyjaszewski
Summary: ATRP is a powerful method for synthesizing polymers with controlled molecular weight, dispersity, and block copolymer formation, leading to unique microstructures and properties. Tuning the dispersity of polymer brushes can result in hybrid materials with special properties.
Article
Polymer Science
Yuanzhang Jiang, Xuyi Wang, Yanting Han, Dakai Gong, Yingchun Gu, Lin Tan
Summary: In this study, FeCl3 and poly(acrylic acid) (PAA) were doped into waterborne polyurethanes (WPUs) to create multifunctional materials with self-healing and antimicrobial properties. WPU/Fe/PAA-5.5, containing 5.5 wt % PAA, exhibited excellent mechanical properties, strong self-healing capabilities, and an impressive antimicrobial rate of over 90%. These supramolecular films were also highly recyclable through hot-pressing.
Article
Polymer Science
Longyu Tian, Min Wang, Guangming Liao, Baoliang Liu, Sujuan Zhang, Yucheng Sun, Zhen Meng, Jintao Zhang, Zaijun Lu
Summary: Two kinds of benzoxazine monomers were synthesized and used to prepare polybenzoxazine anion exchange membranes (AEMs) with quaternary ammonium functionalization. The LQPBZ AEM exhibited better ion conductivity and alkaline stability.
Article
Polymer Science
Claire A. Lemarchand
Summary: This study investigates the shock behavior of three different polymers through molecular dynamics simulations. The results reveal specificities in the shock behavior of polymers, including deviations from the linear relation between shock velocity and particle velocity, as well as differences in shear stress relaxation behind the shock front. It is found that the deviation of the Hugoniot locus is related to the change in the relative contribution of bonding and non-bonding potential energies, while polymers with higher glass transition temperatures exhibit slower shear stress relaxation.
Article
Polymer Science
Zengquan Liu, Xiaochun Yin, He Zhang, Shuo Gao, Qinglin Kuang, Yanhong Feng
Summary: A powder solid-state extension (PSSE) technology was proposed to address the high melt viscosity issue of UHMWPE. By uniaxial extension and sintering in the solid state, a highly self-reinforced material was prepared. X-ray diffraction and scattering techniques were used to study the structural evolution during the PSSE process, and a solid-phase induced transformation model was established.
Article
Polymer Science
Zhike Li, Anyu Luo, Rui Zhou, Xin Li, Haiyan Li
Summary: A novel high temperature resistance IL@SiO2 nanocapsules were successfully prepared and their friction and wear properties in PA6 composites were studied. The addition of IL@SiO2 nanocapsules reduced the friction coefficient and wear rate without affecting the mechanical properties of PA6. The synergy between the IL core and SiO2 wall in the nanocapsules improved the self-lubricating performance of the PA6 composites.
Article
Polymer Science
Xin Liu, Xuhong Guo, Qi Liao
Summary: In this study, an algorithm for accurately estimating viscosity is developed using molecular dynamics simulations and the Green-Kubo formula. This algorithm can be applied to complex systems with long correlations, such as macromolecular and biological simulation systems.
Article
Polymer Science
Hao Pu, Yun-Lei Hou, Jing -Zhou Chen, Dong -Lin Zhao
Summary: The use of modified graphene improves the interfacial adherence of carbon fibers to epoxy resin, resulting in enhanced interfacial and bending properties of CF and matrix in CF/EP composites, as well as increased interlaminar shear strength and flexural strength.
Article
Polymer Science
Wei-Chung Ke, Jin-Wei Lin, Manohar Reddy Busireddy, Yueh-Hsing Lee, Jiun-Tai Chen, Chain-Shu Hsu
Summary: This study introduces a crosslinkable monomer, TAIC, to synthesize three crosslinked polyimide films, which exhibit improved thermal, mechanical, and dielectric properties. The introduction of TAIC enhances the tensile strength, reduces the dielectric constant and dielectric loss, and decreases the coefficient of thermal expansion of the polyimide films.
Article
Polymer Science
Alex Kwasi Kumi, Ruiling Fan, Ye Chen, Yumei Zhang
Summary: The difference in leaching of amylopectin from cellulose/amylopectin/1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) blends during regeneration in water and aqueous ethanol has been studied. Molecular dynamics simulations showed that the dissolution and regeneration mechanisms of amylopectin in [Bmim][Cl] are similar to cellulose in ionic liquids. Water regeneration leads to weak electrostatic interactions, resulting in high leaching of amylopectin. In contrast, ethanol-water interactions enhance electrostatic interactions among amylopectin chains, limiting amylopectin leaching in aqueous ethanol.
Article
Polymer Science
Xi Zeng, Junwei Zhou, Junbiao Peng, Chunsheng Zhang, Danling Wang, Yihu Song, Qiang Zheng
Summary: This study utilizes an oligomer deep eutectic solvent (DES) based on polyethylene glycol to regulate the vulcanization kinetics of rubber. The results show that the DES can accelerate vulcanization at low temperatures without affecting the crosslinking density and Mullins effect.
Article
Polymer Science
Qianqian Yue, Yongfei Peng, Xingjian Liu, Aihua He, Huarong Nie
Summary: The addition of metal deactivators can effectively suppress the aging of TBIR, prolong its lifespan, and have no negative effects on its physical and processing properties. These research findings are of great importance for improving the stability and aging resistance of polymers.
Article
Polymer Science
J. Gomez-Caturla, J. Ivorra-Martinez, R. Tejada-Oliveros, V Moreno, D. Garcia-Garcia, R. Balart
Summary: This work focuses on the development of environmentally friendly PLA formulations by using different esters derived from geraniol as plasticizers. The results show that these esters have good compatibility with PLA, and they can effectively enhance the elongation and plasticity of PLA, reduce its glass transition temperature, and slightly improve its water absorption capabilities.
Article
Polymer Science
Dandan Li, Zhaohui Lu, Zhao Ke, Ke Xu, Fengna Dai, Youhai Yu, Guangtao Qian, Chunhai Chen
Summary: In this study, cross-linked PI aerogel membranes with low dielectric constant and high moisture resistance were prepared by co-polymerization and scraping coating technology. The incorporation of fluorinated blocks and benzimidazole ring structures resulted in novel PI aerogel membranes with fascinating dielectric properties and outstanding moisture resistance.
Article
Polymer Science
Zhaoyang Chu, Qing Zhang, Haihua Luo, Han Zhou, Fapei Zhang, Wei Chen, Wenhua Zhang
Summary: Multi-physical fields solution processing strategy is a universal and facile method for preparing various conjugated polymer films and high-performance devices. In this study, we employed a combined microfluidic flow and ultrasonication strategy (FU) for processing CP solutions, and found a pronounced synergetic effect in promoting the pre-ordering of chains in solution. The conformation order and anisotropy of the solution were revealed through various characterizations. A non-classical nucleation model for polymer crystallization in non-equilibrium solution processing was confirmed. The roles of microfluidic flow and ultrasonication in chain aggregation and crystallization were addressed through multi-physical simulations. Compared to pristine solutions, the FU strategy showed improved solution anisotropy and crystallization kinetics, resulting in higher crystallinity in films and increased mobilities in OFET devices. The FU processing strategy provides a universal approach for regulating chain conformation and aggregation in conjugated polymer solutions.
