Understanding the UCST-type transition of P(AAm-co-AN) in H2O and D2O: dramatic effects of solvent isotopes

Application of a novel and green temperature-responsive deep eutectic solvent system to simultaneously extract and separate different polar active phytochemicals from Schisandra chinensis (Turcz.) Baill

In the present study, a novel and green temperature-responsive deep eutectic solvent (TRDES) system was developed and applied for the simultaneous extraction and separation of different polar active phytochemicals from Schisandra chinensis (Turcz.) Baill. The TRDES, consisting of amino alcohols and phenolic compounds, was chosen as the switching medium, and an upper critical solution temperature (UCST) type switchable solvent was obtained by adding an inorganic salt solution. The switchable phase diagram was plotted based on the relationship between the phase change temperature, the concentration and the amount of sodium chloride solution. Under optimal parameters, the yields with TRDES for different polar active phytochemicals (lignanoids and polysaccharides) from the dried fruit of Schisandra chinensis (DFSC) were 1.62 ∼ 1.17-fold and 1.39-fold to those with conventional solvents. Also, the TRDES system was still effective on extraction of DFSC lignanoids and polysaccharides after four cycles of extraction. The separated polysaccharides and lignanoids both had strong antioxidant activities with IC₅₀ values of 1.92 mg/ mL and 0.10 mg/ mL against 2,2'-Azinobis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS), respectively. The extraction mechanism of TRDES was postulated by Density functional theory (DFT) calculations the hydrogen bonding in TRDES was the main factor to the higher extraction yield. This temperature-responsive deep eutectic solvent could be widely used for the efficient extraction and separation of multi-polar components. As a green and recyclable solvents, TRDES has great potential for the lower cost production from plants.

Theoretical Derivation of the Effect of Bonding Current on the Bonding Interface during Anodic Bonding of PEG-Based Encapsulation Materials and Aluminum

This study analyzed the mechanism underlying the effect of the bonding current on the bonding interface during anodic bonding on the basis of the anodic bonding of PEG (polyethylene glycol)-based encapsulation materials and Al. By establishing an equivalent electrical model, the effects of various electrical parameters on the dynamic performance of the bonding current were evaluated, and the change law of the bonding current transfer function was analyzed. By examining the gap deformation model, the conditions for contact between the interface gaps and the bonding current pair were determined, and the influence law of the gap deformation of the bonding interface was derived. By assessing the effect of the bonding current on the ionic behavior, we found that the larger the bonding current, the greater the number of activated mobile ions in the bonding material and the higher the field strength in the cation depletion area. From the anodic bonding experiments, it was found that increasing the bonding voltage can increase the peak current and improve the bonding efficiency. The SEM image after bonding shows that the bonding interface had no obvious defects; the higher bonding voltage can result in a thicker bonding layer.

Effect of Surface Cleaning Process on the Wafer Bonding of Silicon and Pyrex Glass

Anodic bonding is a reliable packaging method for MEMS devices, and the surface properties of the wafer directly affect the bonding efficiency. Therefore, the surface treatment of the wafer to be bonded is necessary. Herein, the effects of three different surface cleaning processes (degreasing, piranha solution and RCA solution) on the wafer surface were investigated by atomic force microscopy, scanning electron microscopy, infrared spectroscopy, and anodic bonding experiments. The analysis showed that during the anodic bonding of the RCA solution-cleaned wafer and Pyrex glass, the bonding interface was more closely attached, and the best surface properties were obtained. The anodic bonding experiments of the wafer and Pyrex glass showed that the bonding current increased with the applied voltage, and the bonding time decreased accordingly. This was most evident in the case of RCA cleaning. The SEM images showed that as the bonding voltage increased, the bonding interface became more uniform without obvious voids. Due to the influence of the strong electric field and temperature field, an irreversible chemical reaction occurred at the bonding interface, which formed a bonding layer that was key to successful bonding.

Gold-based nanoparticles realize photothermal and photodynamic synergistic treatment of liver cancer and improve the anaerobic tumor microenvironment under near-infrared light

In order to solve the different pains caused by traditional cancer treatment methods such as surgical treatment, the nano-drug delivery system provides new ideas for cancer treatment. In this paper, a novel anti-tumor therapy nanoparticle, P(AAm-co-AN)-AuNRs@CeO2-Ce6(PA/Ce6), is prepared, which provides a novel idea for liver cancer treatment. The CeO2-coated gold nanorods were grafted onto the surface of the temperature-sensitive polymer P(AAm-co-AN)-CTPD. The photosensitizer Ce6 is loaded on the surface of the nanoparticles and the polymer layer. CeO2 can effectively alleviate the tumor anaerobic microenvironment, and under 808 nm near-infrared (NIR) excitation, the gold nanorods achieve photothermal conversion to induce local heating, which leads to the phase transition of the polymer layer and realizes a controllable release mechanism. In addition, 660 nm NIR light can effectively induce Ce6 to produce singlet oxygen, thereby effectively killing cancer cells. Under the 808 nm laser irradiation within 600 s, the PA/Ce6 solution can heat up to about 60°C, which was enough to ablate both cancer cells and tumor tissues. When the temperature was 50°C, the cumulative release rate of Ce6 was 95.31%. Under the 808 nm laser irradiation, oxygen production capacity of PA/Ce6 was higher and can effectively reduce the content of hydrogen peroxide in cancer cells. Compared to free Ce6, the reactive oxygen species-mediated fluorescence of PA/Ce6 nanoparticles was greater. The cell viability and migration of HepG2 cells were decreased after the 660 and 880 nm lasers were irradiated at the same time. The cancer cells were further inhibited, showing a good in vitro anti-tumor effect. PA-DOX showed the best tumor growth inhibitory effect under NIR laser irradiation and had no acute toxicity in vivo. Due to the existence of AuNRs, nanoparticles had high-efficiency photothermal conversion ability to achieve photothermal therapy. Ce6 can generate singlet oxygen under the excitation of 660 nm laser to realize photodynamic therapy. The experimental results also showed that PA/Ce6 can effectively decompose hydrogen peroxide under laser irradiation, aiming to effectively alleviate the anaerobic microenvironment of tumors. These indicate that PA/Ce6 plays a promising role for hepatocellular carcinoma treatment.

Design of a UCST Polymer with Strong Hydrogen Bonds and Reactive Moieties for Facile Polymer-Protein Hybridization

Polymer-protein hybrids have been extensively used in biomedical fields. Polymers with upper critical solution temperature (UCST) behaviors can form a hydrated coacervate phase below the cloud point (T_cp), providing themselves the opportunity to directly capture hydrophilic proteins and form hybrids in aqueous solutions. However, it is always a challenge to obtain a UCST polymer that could aggregate at a high temperature at a relatively low concentration and also efficiently bind with proteins. In this work, a UCST polymer reactive with proteins was designed, and its temperature responsiveness and protein-capture ability were investigated in detail. The polymer was synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylamide (AAm) and N-acryloxysuccinimide (NAS). Interestingly, taking advantage of the partial hydrolysis of NAS into acrylic acid (AAc), the obtained P(AAm-co-NAS-co-AAc) polymer exhibited an excellent UCST behavior and possessed good protein-capture ability. It showed a relatively higher T_cp (81 °C) at a lower concentration (0.1 wt %) and quickly formed polymer-protein hybrids with high protein loading and without losing protein bioactivity, and both the polymer and polymer-protein nanoparticles showed good cytocompatibility. All the findings are attributed to the unique structure of the polymer, which provided not only the strong and stable hydrogen bonds but also the quick and mild reactivity. The work offers an easy and mild strategy for polymer-protein hybridization directly in aqueous solutions, which may find applications in biomedical fields.

RAFT-Polymerized N-Cyanomethylacrylamide-Based (Co)polymers Exhibiting Tunable UCST Behavior in Water

In this present work, the synthesis of a new family of upper critical solution temperature (UCST)-thermoresponsive polymers based on N-cyanomethylacrylamide (CMAm) is reported. It is demonstrated that the thermally initiated reversible addition fragmentation chain transfer (RAFT) polymerization of CMAm conducted in N,N-dimethylformamide (DMF) is well controlled. The homopolymer presents a sharp and reversible UCST-type phase transition in pure water with a very small hysteresis between cooling and heating cycles. It is demonstrated that the cloud point (T_CP ) of poly(N-cyanomethylacrylamide) (PCMAm) is strongly molar mass dependent and shifts toward lower temperatures in saline water. Moreover, the transition temperature can be tuned over a large temperature range by copolymerization of CMAm with acrylamide or acrylic acid. The latter copolymers are both thermoresponsive and pH responsive. Interestingly, by this strategy sharp and reversible UCST-type transitions close to physiological temperature can be reached, which makes the copolymers extremely interesting candidates for biomedical applications.

One-Step Fabrication of a Micro/Nanosphere-Coordinated Dual Stimulus-Responsive Nanofibrous Membrane for Intelligent Antifouling and Ultrahigh Permeability of Viscous Water-in-Oil Emulsions

Membrane fouling is a major challenge for long-term oil/water separation. The incomplete degradation of organic pollutants or membrane damage exists in the common methods of membrane regeneration. Herein, a dual-responsive nanofibrous membrane with high water-in-oil emulsion separation efficiency and smart cleaning properties is reported, which shows complete restoration of its original separation performance. The pH-responsive and upper critical solution temperature (UCST)-type thermoresponsive nanofibrous membrane with a micro/nanosphere structure was developed via a one-step-blending electrospinning strategy. The membrane displays high hydrophobicity/oleophilicity at pH 7 and 25 °C and hydrophilicity/oleophobicity at pH 3 and 55 °C. As a result, it exhibits an ultrahigh permeability of 60528.76 L m^-2 h^-1 bar^-1 and a separation efficiency of 99.5% for water-in-D5 emulsions at room temperature (25 °C). Moreover, the contaminated membranes could be easily reclaimed by being rinsed with warm acidic water (pH 3 and 55 °C). The membrane maintained high separation performance after being used for multiple cycles, indicating its scalable application for purifying emulsified oil. This study provides a facial method of constructing membranes with multiscale hierarchical structures and a new idea for the design of recyclable oil/water separation membranes.

Sulfobetaine-based polydisulfides with tunable upper critical solution temperature (UCST) in water alcohols mixture, depolymerization kinetics and surface wettability

HYPOTHESIS

Synthesis of a new family of polymers having a polydisulfide structure can be conducted from sulfobetaine-based derivative of natural (R)-lipoic acid. A polydisulfide backbone of polymer can be depolymerized by response to external stimuli and sulfobetaine pendant groups ensure the upper critical solution temperature (UCST) behaviour temperatures that can be modulated according to the nature of the solvent and concentration.

EXPERIMENTS

Sulfobetaine-bearing polydisulfides were synthesized from dithiolane derivatives and then characterized. UCST behavior of the polymers in water and in mixtures containing different alcohols (methanol, ethanol, isopropanol) was investigated. The regeneration of monomers from the polymers in response to external stimuli was examined using UV-vis and circular dichroism (CD) spectroscopy. Tunable surface wettability were shown on the grafted polymers.

FINDINGS

Decreasing polarity and/or increasing alcohol percentage in the water mixtures induced an increase in the cloud points of the polymers in the solutions. Thermoresponsive behaviour were repeatable and fully reversible with negligible hysteresis from aggregate to unimer state. The regeneration of monomers by depolymerization was tunable by temperature and sunlight. A thickness dependence on surface wettability was observed on wafers covalently modified with polydisulfides. This is the first report of sulfobetaine-based polydisulfides showing tunable UCST behavior and surface wettability.

A Near-Infrared Laser-Triggered Size-Shrinkable Nanosystem with In Situ Drug Release for Deep Tumor Penetration

The development of smart size-tunable drug delivery nanoplatform enables the solving of the paradox of inconsistent size-dependence of high tumor accumulation and deep penetration during its delivery process, thus achieving superior cancer treatment efficacy. Herein, we report a size-shrinkable nanomicelle complex system with an initial size of 101 nm enabling effective retention around the tumor periphery and could destruct to ultrasmall nanomicelles triggered by a near-infrared (NIR) laser to realize the deep tumor penetration. The nanomicelle system is consisted of an upper critical solution temperature (UCST)-type block copolymer poly(acrylamide-acrylonitrile)-polyethylene glycol-lipoic acid (p(AAm-co-AN)-g-PEG-LA) encapsulating gold nanorods. Upon the irradiation of the NIR laser at the tumor site, gold nanorods could convert the light energy to heat energy, realizing the photothermal ablation of superficial tumor tissue. Concurrently, the large micelles split into a cascade of ultrasmall micelles (∼7 nm), which could easily penetrate into the deep site of the tumor and achieve the in situ "on-demand" release of the loaded drug to exert superior combined photothermal-chemotherapy of cancer. By the precise manipulation of laser, the micelle complex system realized the hierarchical killing from the superficial-to-deep tumor and achieved almost complete tumor growth inhibition on the established xenograft liver tumor mice model.

Highly Bidirectional Bendable Actuator Engineered by LCST-UCST Bilayer Hydrogel with Enhanced Interface

Thermoresponsive hydrogel-based actuators are highly important for fundamental research and industrial applications, while the preparation of temperature-driven bilayer hydrogel actuators with rapid response to bend and recover properties remains a challenge. To date, most temperature-driven bilayer hydrogel actuators are based on polymers only with a lower critical solution temperature (LCST) or with an upper critical solution temperature (UCST), which need more time to bend and recover just in a small range of bending angle. Herein, we propose a new strategy to design and synthesize a fully temperature-driven bilayer hydrogel actuator, which consists of a poly(N-acryloyl glycinamide) (NAGA) layer with a UCST-type volume phase change and a poly(N-isopropyl acrylamide) (NIPAM)-Laponite nanocomposite layer with an LCST-type volume phase change. Due to the complementary UCST and LCST behavior of the two selected polymers, both layers have opposite thermoresponsive swelling and shrinkage properties at low and high temperatures; this imbues the hydrogel actuator with rapid thermoresponsive bending and recovery ability, as well as a large bending angle. In addition, the incorporation of Laponite nanosheets in PNIPAM layer not only improves the mechanical property of actuators but also provides the excellent bonding ability of the two-layer interface, which prevents delamination caused by excessive local stress on the interface during the bending process. Thanks to high-performance behavior, the actuator can act as an effective and sensitive actuator, such as a gripper to capture, transport, and release an object, or as an electrical circuit switch to turn on and off a light-emitting diode (LED). Overall, such hydrogel actuator may provide new insights for the design and fabrication of artificial intelligence materials.

Near-infrared light-responsive UCST-nanogels using an efficient nickel-bis(dithiolene) photothermal crosslinker

A new kind of near-infrared (NIR) light-responsive polymer nanogel is demonstrated.

Thermoresponsive properties of poly(acrylamide-co-acrylonitrile)-based diblock copolymers synthesized (by PISA) in water

UCST-type poly(acrylamide-co-acrylonitrile) diblock copolymers synthesized in water (by PISA) can not only undergo reversible temperature-induced chain dissociation, but also temperature-induced morphological transition.

Multiple-Responsive and Amphibious Hydrogel Actuator Based on Asymmetric UCST-Type Volume Phase Transition

Thermoresponsive hydrogel actuators have attracted tremendous interest due to their promising applications in artificial muscles, soft robotics, and flexible electronics. However, most of these materials are based on polymers with lower critical solution temperature (LCST), while those from upper critical solution temperature (UCST) are rare. Herein, we report a multiple-responsive UCST hydrogel actuator based on the complex of poly(acrylic acid) (PAAc) and poly(acrylamide) (PAAm). By applying a heterogeneous photopolymerization, a bilayer hydrogel was obtained, including a layer of the interpenetrating network (IPN) of PAAm/PAAc and a layer of a single network of PAAm. When cooled down below the UCST, the PAAm/PAAc layer contracted due to the hydrogen bonding of the two polymers while the PAAm layer stays in swelling state, driving the hydrogel to curl. By adjusting the composition of the two layers, the amplitude of actuation behavior could be regulated. By creating patterned IPN domains with photomasks, the hydrogel could deform into complex two-dimensional (2D) and three-dimensional (3D) shapes. An active motion was realized in both water and oil bath, thanks to the internal water exchange between the two layers. Interestingly, the hydrogel actuator is also responsive to urea and salts (Na₂SO₄, NaCl, NaSCN), due to that the strength of the hydrogen bonds in the IPN changes with the additives. Overall, the current study realized an anisotropic UCST transition by introducing asymmetrically distributed polymer-polymer hydrogen bonds, which would inspire new inventions of intelligent materials.

The crucial role of macromolecular engineering, drug encapsulation and dilution on the thermoresponsiveness of UCST diblock copolymer nanoparticles used for hyperthermia

Poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)), an upper critical solution temperature (UCST)-type copolymer in water, was synthesized by reversible addition fragmentation chain transfer (RAFT) copolymerization and used as a macro-RAFT agent for the polymerization of oligo(ethylene glycol) methyl ether methacrylate (OEGMA) to yield amphiphilic diblock P(AAm-co-AN)-b-POEGMA copolymer. A series of copolymers with different AN content was obtained allowing to finely tune the UCST behavior (cloud point (T_t-UCST) from 35 to 78 °C). Addition of the POEGMA block did not modify the T_t-UCST regardless its Mn but provided a lower critical solution temperature behavior at high temperature. Nanoparticles were then formulated by the nanoprecipitation technique revealing that copolymers with higher T_t-UCST yield smaller, better-defined nanoparticles. Eventually, doxorubicin (Dox) was encapsulated into nanoparticles made from the copolymer having a T_t-UCST close to mild hyperthermia (~43 °C). Surprisingly, Dox encapsulation increased T_t-UCST and gave smaller nanoparticles as opposed to their unloaded counterparts. The dilution of the suspension also led to a decrease of Tt-UCST. No obvious hyperthermia effect was observed on the cytotoxicity of Dox-loaded nanoparticles. Our study highlighted the influence of macromolecular engineering, drug encapsulation and nanoparticle dilution on UCST behavior, important features often overlooked despite their crucial impact in the development of thermosensitive nanoscale drug delivery systems.

Upper Critical Solution Temperature (UCST) Behavior of Polystyrene-Based Polyampholytes in Aqueous Solution

Strong polyampholytes comprising cationic vinylbenzyl trimethylammonium chloride (VBTAC) bearing a pendant quaternary ammonium group and anionic sodium p-styrenesulfonate (NaSS) bearing a pendant sulfonate group were prepared via reversible addition-fragmentation chain-transfer polymerization. The resultant polymers are labelled P(VBTAC/NaSS)n, where n indicates the degree of polymerization (n = 20 or 97). The percentage VBTAC content in P(VBTAC/NaSS)n is always about 50 mol%, as revealed by ¹H NMR measurements, meaning that P(VBTAC/NaSS)n is a close to stoichiometrically charge-neutralized polymer. Although P(VBTAC/NaSS)n cannot dissolve in pure water at room temperature, the addition of NaCl or heating solubilizes the polymers. Furthermore, P(VBTAC/NaSS)n exhibits upper critical solution temperature (UCST) behavior in aqueous NaCl solutions. The UCST is shifted to higher temperatures by increasing the polymer concentration and molecular weight, and by decreasing the NaCl concentration. The UCST behavior was measured ranging the polymer concentrations from 0.5 to 5.0 g/L.

Tunable Surface Plasmon Resonance-Based Remote Actuation of Bimetallic Core-Shell Nanoparticle-Coated Stimuli Responsive Polymer for Switchable Chemo-Photothermal Synergistic Cancer Therapy

New dual light/temperature-responsive nanocarriers were synthesized using bimetallic plasmonic Au-Ag and Ag-Au nanoparticles (NPs) as cores of vehicles which subsequently functionalized with an upper critical solubility temperature-based poly acrylamide-co-acrylonitrile using reversible addition-fragmentation chain transfer for spatiotemporally controlled chemo-photothermal synergistic cancer therapy. The bimetallic cores were assigned to sense wavelengths close to the localized surface plasmon resonance of monometallic NP shell to produce heat which not only can increase the surrounding temperature over the upper critical solubility temperature of polymer to open its valves and promote drug diffusion but also can kill cancerous cells through photothermal effects with increase in environment temperature by nearly 18°C after about 5 min radiation. The bimetallic NPs were shown good reusability even after 5 heating/cooling cycles, and the efficiency of both photothermal/chemotherapic procedures can be modulated by manipulating carrier's concentration and radiation time. In addition, the cytotoxicity of drug-free nanocarriers on normal L929 fibroblast and letrozole-loaded nanocarriers on MDAMB 231 breast-cancer cell lines were investigated in the absence/presence of laser radiation. Finally, the prepared nanocomposites were exhibited switchable on/off drug release in 2 buffered solutions (pH 5.5 and 7.4) with light actuation. The results revealed that the prepared nanocarriers can be served as efficient delivery platforms for remote-control chemophotothermal synergistic cancer therapy.

Hyperbranched Multiarm Copolymers with a UCST Phase Transition: Topological Effect and the Mechanism

A novel thermoresponsive hyperbranched multiarm copolymer with a hydrophobic hyperbranched poly[3-ethyl-3-(hydroxymethyl)oxetane] core and many poly(acrylamide- co-acrylonitrile) (P(AAm- co-AN)) arms was for the first time synthesized through a reversible addition-fragmentation chain-transfer polymerization. These copolymers show reversible, sharp, and controlled temperature-responsive phase transitions at the upper critical solution temperature (UCST) in water and electrolyte solution. It is the first report on the hyperbranched copolymers with a UCST transition. Two series copolymers with variable AN content (series A) and variable arm length (series B) were synthesized to study the influence of molecular structure on the UCST transition. It was found that the UCST of copolymers could be raised by increasing the AN content or decreasing the arm length. Most interestingly, the amplification effect of the hyperbranched topological structure leads to a broad change of the UCST from 33.2 to 65.2 °C with the little change of AN content (5.9%). On the basis of variable temperature nuclear magnetic resonance, dynamic light scattering, and transmission electron microscopy, a UCST transition mechanism, in combination with hydrophilic/hydrophobic balance and multimicelle aggregate (MMA), was proposed. This work enriches the UCST copolymer topology and may extend the knowledge on the structure-activity relationship as well as the mechanism of the UCST polymers.

Polyacrylamide "revisited": UCST-type reversible thermoresponsive properties in aqueous alcoholic solutions

Combining experiments and all-atom molecular dynamics simulations, we study the conformational behavior of polyacrylamide (PAM) in aqueous alcohol mixtures over a wide range of temperatures. This study shows that even when the microscopic interaction is dictated by hydrogen bonding, unlike its counterparts that present a lower critical solution temperature (LCST), PAM shows a counterintuitive tunable upper critical solution temperature (UCST)-type phase transition in water/alcohol mixtures that was not reported before. The phase transition temperature was found to be tunable between 4 and 60 °C by the type and concentration of alcohol in the mixture as well as by the solution concentration and molecular weight of the polymer. In addition, molecular dynamics simulations confirmed a UCST-like behaviour of the PAM in aqueous alcoholic solutions. Additionally, it was observed that the PAM is more swollen in pure alcohol solutions than in 80% alcoholic solutions due to θ-like behaviour. Additionally, in the globular state, the size of the aggregates was found to increase with increasing solvent hydrophobicity and polymer concentration of the solutions. Above its phase transition temperature, PAM might be present as individual polymer chains in the coil state (≤10 nm). As PAM is a widespread polymer in many biomedical applications (gel electrophoresis, etc.), this finding could be of high relevance for many more practical applications in high performance pharmaceuticals and/or sensors.

Nanogel-like UCST triblock copolymer micelles showing large volume expansion before abrupt dissolution

A comprehensive study of the thermally induced large expansion in volume prior to the abrupt dissociation of the micelles of a novel UCST triblock copolymer.

Hydrogen bonding reinforcement as a strategy to improve upper critical solution temperature of poly(N-acryloylglycinamide-co-methacrylic acid)

HB-type copolymers with suitably tunable UCST and corresponding core–shell nanogels showing UCST–LCST type behavior.

A molecular level study of the phase transition process of hydrogen-bonding UCST polymers

A molecular level study of the UCST-type transition process of PNAGA-based polymers in water and a water/methanol mixture.

Dielectric analysis of the upper critical solution temperature behaviour of a poly(acrylamide-co-acrylonitrile) copolymer system in water

A copolymer consisting of acrylamide (AAm) and acrylonitrile (AN) in aqueous solution was investigated using broadband dielectric spectroscopy at frequencies between 10^-1 Hz and 10⁶ Hz in the temperature range from 2 °C to 60 °C. This system shows an UCST phase behavior. The phase transition and aggregation behavior is monitored by both the temperature and frequency dependence of the complex conductivity σ*(f, T), where the AN fraction and the concentration of the solution were varied. Additionally, the dielectric data are compared with the results obtained from dynamic light scattering measurements. The temperature dependence of the DC conductivity (σ_DC) of the copolymer solution is monitored and the phase transition temperature (PTT) of the poly(AAm-co-AN) copolymer is deduced from a change in the T-dependence of the DC conductivity. The change in σ_DC can be explained by decreased effective charge carrier mobility and a reduction of the effective charge number density at temperatures below the phase transition temperature of the poly(AAm-co-AN) solution. A pronounced interfacial polarization effect on the frequency dependence of the real part of the conductivity (σ') is observed at temperatures below the phase transition temperature. The charge carriers are blocked at the formed aggregates giving rise to this interfacial polarization. The dependence of the interfacial polarization on the acrylonitrile fraction in the copolymer and the concentration of the solution is studied in detail and conclusions concerning the internal structures of the copolymer aggregates are drawn.

Phase transition and aggregation behaviour of an UCST-type copolymer poly(acrylamide-co-acrylonitrile) in water: effect of acrylonitrile content, concentration in solution, copolymer chain length and presence of electrolyte

An UCST-type copolymer of acrylamide (AAm) and acrylonitrile (AN) (poly(AAm-co-AN)) was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization and its temperature-induced phase transition and aggregation behaviour studied by turbidimetry, static and dynamic light scattering, small angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM) measurements. The phase transition temperature was found to increase with increasing AN content in the copolymer, concentration of the solutions and copolymer chain length. A significant effect was observed onto the phase transition temperature by addition of different electrolytes into the copolymer solution. The copolymer chains were aggregated below the phase transition temperature and disaggregated above it. The size of the aggregates increases with increasing AN contents and concentration of the copolymer solutions below the phase transition temperature. The copolymer chains were expanded and weekly associated in solution above the phase transition temperature. A model is proposed to explain such association-aggregation behaviour of poly(AAm-co-AN) copolymers depending on AN contents and concentration of the copolymer solutions as a function of temperature.

Thermoresponsive functional polymers based on 2,6-diaminopyridine motif with tunable UCST behaviour in water/alcohol mixtures

Two thermoresponsive polyacrylamides based on the 2,6-diaminopyridine motif were synthesized and their UCST-type reversible thermoresponsive behaviour was studied in water/alcohol mixtures.

Modulating the solubility of zwitterionic poly((3-methacrylamidopropyl)ammonioalkane sulfonate)s in water and aqueous salt solutions via the spacer group separating the cationic and the anionic moieties

Even small variations of the spacer group between the anionic and the cationic moieties of poly(sulfobetaine)s strongly affect their aqueous phase behaviour.

On the abnormal “forced hydration” behavior of P(MEA-co-OEGA) aqueous solutions during phase transition from infrared spectroscopic insights

During the phase separation of POEGA in water, C–H groups exhibit dehydration, whereas CO and C–O–C groups present “forced hydration”.

What determines the volume transition temperature of UCST acrylamide–acrylonitrile hydrogels?

The positive thermosensitivity of a hydrogel composed of acrylamide and acrylonitrile was investigated, and the parameters that determine the hydrogel's volume transition temperature were identified.

Thermoreversible physically crosslinked hydrogels from UCST-type thermosensitive ABA linear triblock copolymers

Moderately concentrated aqueous solutions of UCST-type thermosensitive ABA linear triblock copolymers undergo cooling-induced, reversible sol–gel transitions.

pH dependent thermoresponsive behavior of acrylamide–acrylonitrile UCST-type copolymers in aqueous media

pH-dependent UCST-transitions and influence of sacrificial additives on the thermoresponsivity of acrylamide- acrylonitrile copolymers is shown.