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Open accessJournal ArticleDOI: 10.1039/D0SM01505A

LCST polymers with UCST behavior.

04 Mar 2021-Soft Matter (The Royal Society of Chemistry)-Vol. 17, Iss: 8, pp 2132-2141
Abstract: In this study, temperature dependent behavior of dense dispersions of core crosslinked flower-like micelles is investigated. Micelles were prepared by mixing aqueous solutions of two ABA block copolymers with PEG B-blocks and thermosensitive A-blocks containing PNIPAM and crosslinkable moieties. At a temperature above the lower critical solution temperature (LCST), self-assembly of the polymers resulted in the formation of flower-like micelles with a hydrophilic PEG shell and a hydrophobic core. The micellar core was stabilized by native chemical ligation (NCL). Above the LCST, micelles displayed a radius of ∼35 nm, while a radius of ∼48 nm was found below the LCST due to hydration of the PNIPAM core. Concentrated dispersions of these micelles (≥7.5 wt%) showed glassy state behavior below a critical temperature (Tc: 28 °C) which is close to the LCST of the polymers. Below this Tc, the increase in the micelle volume resulted in compression of micelles together above a certain concentration and formation of a glass. We quantified and compared micelle packing at different concentrations and temperatures. The storage moduli (G') of the dispersions showed a universal dependence on the effective volume fraction, which increased substantially above a certain effective volume fraction of φ = 1.2. Furthermore, a disordered lattice model describing this behavior fitted the experimental data and revealed a critical volume fraction of φc = 1.31 close to the experimental value of φ = 1.2. The findings reported provide insights for the molecular design of novel thermosensitive PNIPAM nanoparticles with tunable structural and mechanical properties.

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Journal ArticleDOI: 10.1016/J.POLYMER.2021.124109
28 Sep 2021-Polymer
Abstract: Smart wrinkled hydrogel patterns with modulated chemical composition and wrinkle characteristics (amplitude and period) were formed by taking advantage of surface instabilities using a simple, cost-affordable, and robust method. The microstructured surfaces were prepared by dip coating and were designed to be stimuli-responsive by introducing poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) in the initial feed. For this purpose, a silylated substrate surface serves as an anchor for the non-polymerized hydrogel molecules, thus forming a homogenous and reproducible coating. Once the film was achieved, the samples were exposed to vacuum and UV irradiation to form wrinkled patterns spontaneously. The response of the thermosensitive wrinkles reveals significant variations in the properties of the wrinkled films depending on the temperature. In addition to the simplicity, this deposition strategy allows the preparation of highly reproducible films using an easy-scalable methodology with potential interest for industrial applications.

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Topics: Dip-coating (55%), Coating (52%)

2 Citations


Journal ArticleDOI: 10.1103/PHYSREVMATERIALS.5.065604
Rui Xiao1, Hai Li2Institutions (2)
Abstract: Recent works have shown that gels with a large amount of solvents can still exhibit a glass transition behavior with the thermomechanical properties exhibiting tremendous change over a narrow temperature region. Similar to dry polymers, the rheological behaviors of gels also show a broad distribution of relaxation times. However, so far the effects of solvents on the relaxation spectrum have rarely been studied. In this work, we first develop a viscoelastic model to relate the rheological properties of gels and the corresponding properties in the dry state. We then apply the theoretical model to analyze the complex modulus of gels measured in the small strain dynamic tests. The results show that the breadth of relaxation spectrum has been expanded by increasing the swelling ratio. The physical mechanism behind this observation needs a deep investigation in further study and also raises a significant challenge for developing constitutive models for gels.

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Topics: Relaxation (physics) (51%), Glass transition (50%)

1 Citations


Journal ArticleDOI: 10.1039/D1SM01178B
Liqian Wang1, Fengrui Liu1, Jin Qian1, Zi Liang Wu1  +1 moreInstitutions (1)
17 Sep 2021-Soft Matter
Abstract: Hydrogels are widely used in applications such as soft robots and flexible sensors due to their sensitivity to environmental stimuli. It is highly demanded to develop multiple-responsive hydrogel structures. In this work, we employ the 3D printing technique to fabricate a PNIPAM–PEGDA hydrogel bilayer that can change shape through controlling the temperature, solvent mixture and magnetic field. The PNIPAM gel is a typical thermo-responsive gel, showing a decrease in swelling ratio with increasing temperature. Meanwhile, the PNIPAM gels also exhibit the cononsolvency effect in ethanol–water mixtures with a smaller swelling ratio in the mixture compared with that in each pure solvent. In comparison, the swelling ratio of PEGDA gels is insensitive to changes in both the temperature and solvent composition. Thus, the bilayer structure of PNIPAM–PEGDA can bend in different directions and with different angles with changing the temperature and solvent composition. Finally, Fe3O4 nanoparticles are incorporated into the matrix of PEGDA gels, endowing the whole structure with deformation and motion in response to an external magnetic field.

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Topics: Self-healing hydrogels (55%), Bilayer (50%)

Journal ArticleDOI: 10.1039/D1MH01091C
01 Jan 2022-Materials horizons
Abstract: Thermoresponsive supramolecular assemblies have been extensively explored in diverse formats, from injectable hydrogels to nanoscale carriers, for a variety of applications including drug delivery, tissue engineering and thermo-controlled catalysis. Understanding the molecular bases behind thermal sensitivity of materials is fundamentally important for the rational design of assemblies with optimal combination of properties and predictable tunability for specific applications. In this review, we summarize the recent advances in this area with a specific focus on the parameters and factors that influence thermoresponsive properties of soft materials. We summarize and analyze the effects of structures and architectures of molecules, hydrophilic and lipophilic balance, concentration, components and external additives upon the thermoresponsiveness of the corresponding molecular assemblies.

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Journal ArticleDOI: 10.1039/D1PY00996F
Yuewen Yu1, Guangran Shao1, Wangqing Zhang1Institutions (1)
12 Oct 2021-Polymer Chemistry
Abstract: For a general responsive polymer exhibiting a thermoresponsive transition in a solvent at the upper critical solution temperature (UCST), the interaction between polymer chains and solvent molecules and the interaction among polymer chains are of vital importance. Here, a new thermoresponsive transition in liquid crystalline poly(11-(4-((E)-4-butylstyryl)phenoxy)undecyl methacrylate) (PMAS) is found. The liquid crystalline PMAS containing mesogen moieties of stilbene in the side chains with a controlled molecular weight and narrow molecular weight distribution is synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization, and it can undergo a sharp and reversible insoluble-to-soluble transition in the solvents toluene, 1,2,4-triethylbenzene, and 1,4-dioxane at an UCST ranging from 26.3 °C to 52.3 °C. Why and how PMAS undergoes a thermoresponsive solubility transition in solvents are revealed, and the conclusion that crystallization drives the thermoresponsive solubility transition is made. It is believed that the crystallization strategy may be utilized to design new thermoresponsive polymers.

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References
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51 results found



Open accessBook
01 Jan 1971-
Abstract: This is a paperback edition of a distinguished book, originally published by Clarendon Press in 1971. It was then the first text on critical phenomena, a field that has enjoyed great activity for the past twenty years and that still continues to attract much attention. The book is at the level at which a graduate student who has studied condensed matter physics can begin to comprehend the nature of phase transitions, which involve the transformation of one state of matter into another. (A simple example is the melting of a solid to become a liquid.) Such a transformation is termed 'critical' when, after a certain amount of the substance changes phase, the entire bulk virtually instantaneously also makes the transition. A second, updated edition is planned for future publication, but in the mean time this paperback reissue will be useful in teaching the fundamental principles of this extremely interesting subject.

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4,766 Citations


PatentDOI: 10.1126/SCIENCE.7973629
04 May 1995-Science
Abstract: Proteins of moderate size having native peptide backbones are produced by a method of native chemical ligation. Native chemical ligation employs a chemoselective reaction of two unprotected peptide segments to produce a transient thioester-linked intermediate. The transient thioester-linked intermediate then spontaneously undergoes a rearrangement to provide the full length ligation product having a native peptide bond at the ligation site. Full length ligation products are chemically identical to proteins produced by cell free synthesis. Full length ligation products may be refolded and/or oxidized, as allowed, to form native disulfide-containing protein molecules. The technique of native chemical ligation is employable for chemically synthesizing full length proteins.

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Topics: Native chemical ligation (80%), Chemical ligation (75%), Peptide chemical synthesis (60%) ... show more

3,347 Citations


Journal ArticleDOI: 10.1080/10601326808051910
M. Heskins1, J. E. Guillet1Institutions (1)
Abstract: Aqueous solutions of poly(N-isopropyl acrylamide) show a lower critical solution temperature. The thermodynamic properties of the system have been evaluated from the phase diagram and the heat absorbed during phase separation and the phenomenon is ascribed to be primarily due to an entropy effect. From viscosity, sedimentation, and light-scattering studies of solutions close to conditions of phase separation, it appears that aggregation due to formation of nonpolar and intermolecular hydrogen bonds is important. In addition, a weakening of the ordering effect of the water-amide hydrogen bonds as the temperature is raised contributes to the stability of the two-phase system.

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2,562 Citations


Journal ArticleDOI: 10.1063/1.1699894
Abstract: In this paper it is shown that the viscosity of the liquid normal paraffins can be accurately defined as a simple function of relative free‐space except for values in the neighborhood of the freezing points of each compound A novel method of extrapolating the specific volumes of this family of compounds to absolute zero is described which permits the calculation of reliable values of the relative free‐space from density dataAn expression of the same form as the author's function, but in which temperature rather than free‐space is the primary variable (the so‐called Andrade equation), fails to reproduce the viscosity of n‐heptadecane over the same range of temperatures within the limits of the known accuracy of the measurements

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Topics: Viscosity (55%), Freezing point (54%), Newtonian fluid (51%)

1,420 Citations