PNIPAM Nanogels Research Articles

Hybrid Nanogel-Wrapped Anisotropic Gold Nanoparticles Feature Enhanced Photothermal Stability.

Anisotropic gold nanoparticles (AuNPs) are renowned for their unique properties - including localized surface plasmon resonance (LSPR) and adjustable optical responses to light exposure - that enable the conversion of light into heat and make them a promising tool in cancer therapy. Nonetheless, their tendency to aggregate and consequently lose their photothermal conversion capacity during prolonged irradiation periods represents a central challenge in developing anisotropic AuNPs for clinical use. To overcome this issue, an innovative approach that facilitates the encapsulation of individual anisotropic AuNPs within thin nanogels, forming hybrid nanomaterials that mirror the inorganic core's morphology while introducing a negligible (2-8nm) increase in overall diameter is proposed. The encapsulation of rod- and star-shaped anisotropic AuNPs within poly-acrylamide (pAA) or poly-(N-isopropylacrylamide) (pNIPAM) nanogels is successfully demonstrated. The ultrathin polymeric layers display remarkable durability, significantly enhancing the photothermal stability of anisotropic AuNPs during their interaction with near-infrared light and effectively boosting their photothermal capacities for extended irradiation periods. The outcomes of the research thus support the development of more stable and reliable AuNPs as hybrid nanomaterials, positioning them as promising nanomedicinal platforms.

Cation-induced morphological transitions and aggregation of thermoresponsive PNIPAM nanogels

Poly(N-isopropylacrylamide) (PNIPAM) nanogels are promising responsive colloidal particles that can be used in pharmaceutical applications as drug carriers. This work investigates the temperature-dependent morphological changes and agglomeration of PNIPAM nanogels in the presence of mono- and multi-valent cationic electrolytes. We described the deswelling, flocculation, thermal reversibility behaviour and aggregated morphology of PNIPAM nanogels over a range of electrolyte concentrations and temperatures revealing the critical transition points from stable suspension to spontaneous agglomeration. We demonstrated that the flocculating ability and the rate of aggregate formation follow the order of deswelling behaviour. Transmission electron microscopy and atomic force microscopy analysis revealed the presence of a shell-like layer with varying density in the multivalent electrolyte solutions when compared to those in aqueous medium. We identified a concentration threshold of the thermally induced reversible aggregation/dispersion for the PNIPAM nanogels in the presence of Na+ and K+ ions at 10 mM, for Mg2+ and Ca2+ ions at 1 mM and for Al3+ ions at 0.1 mM concentrations. Such concentration thresholds indicated the effective destabilization of the electrolyte system with multivalency following the Schulze–Hardy rule. Our findings were supported by applying a Debye screening model that accounts for the shielding effect of multivalent cationic electrolytes on these nanogel systems. Our experiments and the models confirmed the compression of the electric double layer as the valency and ionic strength increased, except for Al3+ at higher concentrations which seemed to disrupt the electrical double layer and cause reversal of zeta potential. Our work highlights the significant impact the presence of multivalent cations can impose on the stability and morphology of nanogels, and this understanding will help in designing responsive nanogel systems based on PNIPAM nanogels.

Synthesis of thermoresponsive PNIPAm nanogel adsorbent by microwave-assisted polymerization for wastewater treatment application

This research demonstrated the fast synthesis technique using microwave-assisted polymerization for the preparation of thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) nanogel which was to be used for paraquat pesticide adsorption. PNIPAm nanogel was synthesized by free-radical polymerization in an aqueous solution using water-soluble ammonium peroxodisulfate (APS) and N,Ń-methylenebisacrylamide (BIS) as initiators and cross-linker, respectively. Microwave irradiation was used as an alternative heating technique and its efficiency was compared to that of the conventional heating method. The results showed that reaction time could be greatly shortened from several hours to only 20 min with the yield of PNIPAm nanogel of approximately 65 % using microwave heating method. The FTIR analysis confirmed that microwave irradiation did not alter the chemical structure of PNIPAm nanogel. The cross-linker concentrations and the sequence of cross-linker addition affected the hydrodynamic diameter of PNIPAm nanogel. The hydrodynamic diameter of swollen PNIPAm nanogels at 25 °C decreased as increasing the cross-linker concentrations and then further decreased when the cross-linker was added after 10 min of the irradiation time. Besides, all PNIPAm nanogel showed well thermoresponsive reversibility over 5 cycles, across the volume phase transition temperature (VPTT) at around 32 °C. The adsorption and release mechanisms of the paraquat took advantage of the phase transition change (swelling-collapse) in response to temperature stimuli, respectively. The PNIPAm nanogel synthesized from the microwave heating method had a profound effect on paraquat adsorption, having 60 – 70 % adsorption with a paraquat release of around 35 – 45 %. These results demonstrated that PNIPAm nanogels could be used as an alternative adsorbent material for industrial wastewater treatment.

Characterization of Ball-milled Poly(Nisopropylacrylamide) Nanogels

Abstract Poly(N-isopropylacrylamide) (PNIPAM) hydrogels are one of the most commonly studied thermoresponsive biomaterials. In this work, we investigate ball milling as a method of producing PNIPAM nanogels and confirm that the temperature responsiveness is maintained in the nanogel form based on hydrodynamic diameter and zeta potential measurements.

Molecularly engineered CMC-caged PNIPAM for broadband light management in energy-saving window

Dynamic transparent-opaque transition behavior endows the stimuli-chromic materials with the solar modulation capability. However, these materials commonly involve the high manufacturing cost and complexity, the additional consumption of electric energy for solar modulation, or the weak effectiveness of light management. Herein, we develop a low-cost yet broadband light management sodium carboxymethyl cellulose-caging-poly(N-isopropylacrylamide) thermochromic composite (i.e., CMC/PNIPAM), where the nanoscale-skeleton CMC molecules well cage the PNIPAM molecules, which enables the homogeneous dispersion and sufficient distribution of the PNIPAM nanogels in the system. The CMC/PNIPAM features the excellent solar-modulation capability (including optical transmittance modulation of 68.17% and infrared transmittance modulation of 48.50%) and a low phase temperature of 30 °C, as well as the long-term stability of dynamic transparent-opaque transition. Such merits of the broadband light management, low cost, simply fabrication as well as scaling up, make the CMC/PNIPAM function as a promising candidate for the energy-saving buildings and construction.

Surfactant-Assisted Synthesis of Pt Nanocubes Using Poly(N-isopropylacrylamide) Nanogels.

Poly(N-isopropylacrylamide) (PNIPAM) nanogels were prepared by emulsion polymerization using sodium dodecyl sulfate (SDS) and employed as a capping agent in platinum nanoparticle (Pt NP) synthesis by liquid-phase reduction with hydrogen gas. When the PNIPAM nanogels were used without removing SDS, that is, a slight amount of SDS was included in the reaction solution, Pt nanocubes (NCs) were predominantly produced (>80%). The proportion of the resultant Pt NCs was much higher than that obtained using the PNIPAM linear polymer (∼60%). To clarify the effects of the three-dimensional polymer network and SDS, we synthesized Pt NPs using the PNIPAM nanogel without SDS (SDS-free PNIPAM nanogel) and found that Pt NCs are rarely formed, and most NPs obtained have an irregular shape. When only SDS was used as a capping agent, NCs were hardly obtained, but other polyhedral NPs were formed. Furthermore, the use of SDS together with the PNIPAM polymer led to the decrease in the proportion of the Pt NCs compared with that obtained using only the linear polymer. These results indicate that the enhancement of the Pt NC proportion using the PNIPAM nanogel with SDS is attributable to not only the three-dimensional polymer network of the PNIPAM nanogel but also the assist of SDS as a capping agent.

Programming Colloidal Self-Assembled Patterns (cSAPs) into Thermo-Responsible Hybrid Surfaces for Controlling Human Stem Cells and Macrophages.

Hybrid surfaces with tunable topography, chemistry, and stiffness have potential to rebuild native extracellular matrix (ECM) and manipulate cell behavior in vitro. However, the fabrication of controllable hybrid surfaces is still challenging. In this study, colloidal self-assembly technology was used to program particles into highly ordered structures with hybrid chemistry and stiffness at biointerfaces. These colloidal self-assembled patterns (cSAPs), including unary, binary, and ternary cSAPs, composed of silicon (Si), polystyrene (PS), and/or poly(N-isopropylacrylamide) (pNIPAM) nanogels (PNGs), were fabricated using either coassembly or layer-by-layer (LBL) methods. The selected binary cSAPs (i.e., PS/PNG and PNG/PS) have a tunable surface topography and wettability between 25 and 37 °C; thus, they can be used as dynamic cell culture substrates. Human adipose-derived mesenchymal stem cells (hASCs), bone marrow-derived mesenchymal stem cells (hBMSCs), and macrophages (THP-1) were investigated on these hybrid cSAPs under a static or dynamic system. The results showed that hybrid cSAPs significantly influenced the focal adhesions, cell morphology, cell migration, and gene expressions of stem cells. In general, stem cells had more vinculin puncta, smaller spreading size, and faster migration speed than the TCPS control. Hybrid cSAPs up-regulated gene expressions of focal adhesion kinase (FAK) and chondrocytes (AGG and SOX9) under static culture, while they also up-regulated osteocytes (COL1 and RUNX2) under dynamic culture. THP-1 macrophages were at M0 state on all cSAPs under static culture. However, cells became sensitive under dynamic culture. For example, some M1 genes (i.e., IL6, CD68, and TNFα) and M2 genes (i.e., IL10 and CD206) were down-regulated, while other M1 genes (i.e., IL1β) and M2 genes (i.e., TGF-β and IL1ra) were up-regulated, depending on the particle combinations. In conclusion, new hybrid cSAPs with thermoresponsive surface properties are versatile materials for stem cells and macrophages manipulation.

Synthesis, characterization and in vitro cytotoxicity studies of poly-N-isopropyl acrylamide gel nanoparticles and films

In this work, we show synthesis that leads to thermoreponsive poly-N-isopropyl acrylamide (pNIPAM) nanogels with sizes below 100 nm, irrespectively of the surfactant to crosslinker ratio. We also show that in many environments the temperature induced pNIPAM collapse at Lower Critical Solution Temperature (LCST) of 32.5 °C is accompanied by gel nanoparticles' aggregation. Thus, the proper information on the nanoparticle (NP) structure and deswelling can be obtained only if the routinely measured hydrodynamic radius is supplemented by information on the molecular weight, which can be obtained from the intensity of scattered light. We measured the dynamics and reversibility of the deswelling and subsequent aggregation processes.Furthermore, we show that the highly concentrated pNIPAM gel NPs reversibly form bulk hydrogel networks of varied interconnected porous structure. We show, that in case of drying pNIPAM gel NPs above the LCST, it is possible to obtain films with 20-fold increase in storage modulus (G′) compared to hydrogel networks measured at room temperature. They exhibit temperature hysteresis behavior around LCST of 32.5 °C similar to pNIPAM films. Finally, we show that these hydrogel films, lead to extended proliferation of cells across three different types: fibroblast, endothelial and cancer cells. Additionally, none of the films exhibited any cytotoxic effects. Our study brings new insights into physicochemical characterization of pNIPAM gel NPs and networks behavior in realistic conditions of in vitro measurements, especially by means of dynamic light scattering as well as final unique properties of both gel NPs and formed porous films for possible tissue engineering applications.

Poly(N-isopropylacrylamide) based thin microgel films for use in cell culture applications

Poly(N-isopropylacrylamide) (PNIPAm) is widely used to fabricate cell sheet surfaces for cell culturing, however copolymer and interpenetrated polymer networks based on PNIPAm have been rarely explored in the context of tissue engineering. Many complex and expensive techniques have been employed to produce PNIPAm-based films for cell culturing. Among them, spin coating has demonstrated to be a rapid fabrication process of thin layers with high reproducibility and uniformity. In this study, we introduce an innovative approach to produce anchored smart thin films both thermo- and electro-responsive, with the aim to integrate them in electronic devices and better control or mimic different environments for cells in vitro. Thin films were obtained by spin coating of colloidal solutions made by PNIPAm and PAAc nanogels. Anchoring the films to the substrates was obtained through heat treatment in the presence of dithiol molecules. From analyses carried out with AFM and XPS, the final samples exhibited a flat morphology and high stability to water washing. Viability tests with cells were finally carried out to demonstrate that this approach may represent a promising route to integrate those hydrogels films in electronic platforms for cell culture applications.

Temperature-Responsive Poly(N-Isopropylacrylamide) Nanogels: The Role of Hollow Cavities and Different Shell Cross-Linking Densities on Doxorubicin Loading and Release.

Smart polymers with extraordinary characteristics are studied in drug-delivery applications. In the current study, temperature-responsive hybrid core-shell nanoparticles were synthesized by precipitation polymerization of N-isopropylacrylamide and vinyl-modified silica nanoparticles. These temperature-responsive hybrid core-shells were prepared with different cross-linking densities by using 2, 4, and 8 mol % of N,N-methylene bisacrylamide (MBA). Hydrolysis of the silica cores of the hybrid core-shells resulted in hollow poly(N-isopropylacrylamide) (PNIPAM) nanogels. Functionalization of silica nanoparticles with vinyl-containing silane modifier of 3-(trimethoxysilyl) propyl methacrylate (MPS) in two different contents was proven by Fourier transform infrared spectroscopy. Preparation of the hybrid PNIPAM nanogels and etching of the silica cores were studied using thermogravimetric analysis and also electron microscopy imaging. Sensitivity of the PNIPAM nanogel samples to temperature was studied using ultraviolet-visible (UV-vis) spectroscopy. In addition, dynamic light scattering was used for investigation of the squeezing and expansion of the hybrid and hollow samples against variation of temperature. The UV-vis spectroscopy results display higher absorption intensities in higher contents of MPS modifier and MBA cross-linker. The swelling content of the nanogels with hollow cavities was higher than that of the hybrid samples. The hybrid nanogels with 2 and 8 wt % silica content and different cross-linking densities and also their hollow nanoparticles were used for loading and release of doxorubicin (DOX). The release characteristics of the DOX-loaded nanogels were studied at different temperatures using UV-vis spectroscopy. The DOX release was higher at temperatures lower than the gel collapse temperature of the PNIPAM network. Although the nanogels with hollow cavities displayed higher loading capacities, the release percentage was higher for the hybrid PNIPAM nanogels, which was confirmed by the experimental release profiles and mathematical models. The most appropriate fitting of the DOX release data from the PNIPAM nanogel samples was observed for the Korsmeyer-Peppas model. Cytotoxicity studies on HeLa cell line showed that drug-loaded hollow samples showed higher toxicity due to loading of a higher amount of DOX.

How small can poly(N-isopropylacrylamide) nanogels be prepared by controlling the size with surfactant?

Despite the increasing demand for ‘as small as possible’ responsive poly(N-isopropylacrylamide) (pNIPAm) nanogels with well-defined internal structure, up to date there is no systematic investigation to provide guidance what are the lower limits of nanogel size and what interactions limit its further decrease. In this work both classical batch precipitation polymerization (at 60, 70 and 80 °C) and monomer-feeding precipitation polymerization (at 80 °C) is used to determine how small pNIPAm particles could be prepared by surfactant addition. The collapsed particle size levels off with increasing surfactant concentration in each case but at a strongly temperature dependent value. The plateau values of the microgel size show non-monotonic temperature dependence. To gain deeper insight into the interactions controlling the variation of microgel size with surfactant concentration and temperature a simple model was developed and fitted to the experimental data. The model fitting clearly showed that microgel size is controlled by two key parameters: the underlying adsorption isotherm of surfactant adsorption on the collapsed microgel particles and the effective initiator concentration (the amount of initiator fragments providing surface charge for the precursor particles in unit volume of reaction mixture). The significance of the formation of carboxylic groups in the polymer network is also discussed.

Hybridization of graphene oxide into nanogels to acquire higher photothermal effects for therapeutic delivery

Although the special architecture of two-dimensional (2D) nanomaterials endows them with unique properties, their poor colloidal stability remains a main bottleneck to fully exploit their applications in the biomedical field. Herein, this study aims to develop a simple and effective approach to in situ incorporate 2D graphene oxide (GO) nanoplatelets into a thermosensitive matrix to acquire hybrid nanogels with good stability and photothermal effect. In order to improve its stability, GO firstly underwent silanization to its surface with double bonds, followed by intercalation with N-isopropylacrylamide (NIPAM) in the presence of a disulfide-containing crosslinker via an emulsion method. Radical polymerization was then initiated to accelerate direct GO exfoliation in PNIPAM nanogels by forming covalent bonds between them. The well-dispersed GO nanopletlets in the nanogels not only displayed an enhanced photothermal effect, but also improved the encapsulation efficiency of an anticancer drug. The hybrid nanogels accelerate drug release under conditions mimicking the acidic/reducible solid tumor and intracellular microenvironments, most importantly, it can be further enhanced via remote photothermal treatment. The multifunctional nanogels potentiate their synergistic anticancer bioactivity as an ideal nanoplatform for cancer treatment.

Nanostructured Thermoresponsive Surfaces Engineered via Stable Immobilization of Smart Nanogels with Assistance of Polydopamine.

Thermoresponsive surfaces featured with nanostructures have found wide potential applications in biological and chemical fields. Herein, we report nanostructured thermoresponsive surfaces engineered via stable immobilization of thermoresponsive nanogels with the assistance of polydopamine. The results show that the thin layer of polydopamine on the poly( N-isopropylacrylamide) (PNIPAM) nanogels nearly does not affect the thermoresponsive property of the nanogels. The stability of the thermoresponsive nanogels on the substrate surfaces immobilized under different pH conditions of dopamine solutions are quatitively studied by fluid shearing experiments inside capillaries, and the characterization results show that the strong interaction forces between the polydopamine layer on the substrate surfaces and the thermoresponsive nanogels are heavily dependent on the oxidation state of the dopamine molecules. With the proposed strategy, thermoresponsive nanostructured surfaces immobilized with PNIPAM nanogels on two-dimensional and three-dimensional substrate surfaces are generated to achieve smart cell culture plates and smart gating membranes, respectively, which demonstrate versatile applications of the nanostructured thermoresponsive surfaces.

Thermoresponsive Three‐Stage Optical Modulation of a Self‐Healing Composite Hydrogel

AbstractA self‐healing composite hydrogel with thermoresponsive three‐stage optical adjustment (opaque‐transparent‐translucent) is achieved by combining polyampholyte hydrogel (PAH) with a small amount of poly(N‐isopropylacrylamide) (PNIPAM) nanogels. The PAH has an upper critical solution temperature to dominate the initial optical stage of reversible opaque‐transparent transition and also offers its self‐healing properties via reversible ionic bonds. Meanwhile, the PNIPAM shows a lower critical solution temperature by hydrophilic‐hydrophobic phase transition and synergistic clustering of PAH, which controls the subsequent optical stage of reversible transparent‐translucent transition. Therefore, the PAH/PNIPAM composite hydrogel shows a reversible three‐stage optical modulation by controlling temperature from low (<15 °C) to medium (15–30 °C) to high (>30 °C) via double phase transition behavior of PAH/PNIPAM. Through different analytical methods, the synergistic thermoreposensive effects of PNIPAM nanogels and the bulk PAH are demonstrated. Finally, a prototype of a smart window is designed to demonstrate one of its potential applications.

Externally Triggered Oscillatory Structural Forces.

This paper addresses triggering of oscillatory structural forces via temperature variation across an aqueous dispersion of thermoresponsive poly( N-isopropylacrylamide) (PNIPAM) nanogels confined between silica surfaces. Oscillatory structural forces are a well-known phenomenon in colloidal science, caused by interactions between molecules or colloids. Modulation of these forces usually requires changing the internal parameters of the dispersion, such as ionic strength, particle concentration, and surface charge, or changing the properties of the confining walls, such as surface roughness, potential, or elasticity. All of these parameters are usually fixed and can only be changed via exchange of the sample or the complete experimental setup. Here, a new approach is presented, combining the characteristics of smart materials with the properties of nanoparticles, using negatively charged PNIPAM nanogels. Aqueous dispersions of these nanogels express no oscillatory structural forces in the initial state (20 °C), below the volume phase transition temperature (32 °C). Heating (60 °C) reduces the nanogel size and leads to a more negative ζ-potential, which triggers the onset of oscillatory structural forces.

Facile synthesis of thermo-responsive nanogels less than 50 nm in diameter via soap- and heat-free precipitation polymerization

Owing to their highly desirable properties that combine the properties of both hydrogels and nanomaterials, smart nanogels own great potentials as active nanocarriers in medical applications. In this paper, thermo-responsive nanogels with uniform sizes less than 50 nm in diameter were synthesized using potassium persulfate (KPS)/N,N,N′,N′-tetramethylethylenediamine (TMEDA) as a initiator system via a facile surfactant-free precipitation radical polymerization of N-isopropylacrylamide (NIPAM) at room temperature. Both transmission electron microscopy and dynamic light scattering were used to characterize the morphologies and diameters of the PNIPAM nanogels. All nanogels with spherical shape exhibited a narrow size distribution, and the finest nanogels were 43 nm in diameter on average. The very fine and highly pure nanogels would be more promising for drug delivery carriers than the bulk gels or microgels.

A Novel Thermoresponsive Catalytic Membrane with Multiscale Pores Prepared via Vapor-Induced Phase Separation.

A novel thermoresponsive catalytic polyethersulfone membrane with multiscale pores is developed by constructing silver nanoparticles (Ag NPs) loaded poly(N-isopropylacrylamide) (PNIPAM) nanogels on pore walls of cellular pores as thermoresponsive gates and catalysts via vapor-induced phase separation. The Ag NPs are stably immobilized on the PNIPAM nanogels by an in situ reduction method based on the versatile adhesion and reduction properties of polydopamine. The micrometer cellular pores decorated with Ag NPs loaded PNIPAM nanogels are formed throughout the membrane and act as numerous microreactors with a large pore surface. The proposed membrane exhibits both satisfactory thermoresponsive characteristics and stable catalytic properties. The effects of operation temperature and reactant concentration of feed solution on the catalytic properties are investigated systematically. The results show that the apparent kinetic rate constant of catalytic reduction of 4-nitrophenol (4-NP) in water by reductant sodium borohydride (NaBH4 ), is ranging from 3.7 to 37.9 min-1 at temperatures from 20 to 45 ºC and the molar ratio of NaBH4 to 4-NP from 100:1 to 500:1. When the reactant concentration in feed solution fluctuates, the permeability or throughput of the membrane is simply adjusted by virtue of the thermoresponsive characteristics of membranes to achieve high catalytic conversion of reactant.

Chitosan-based polymer hybrids for thermo-responsive nanogel delivery of curcumin

The purpose of this study is to design and develop thermoresponsive nano-sized hydrogel particles from a natural polymer, chitosan, as smart material platforms for curcumin delivery. Chitosan was used as the backbone material to be grafted with poly–(N-isopropylacrylamide) (pNIPAM) using an EDC/NHS coupling reaction. The conjugated products were characterized by 1H NMR and TGA. Chitosan-grafted pNIPAM (CS-g-pN) nanogels were prepared by a sonication method. The loading of curcumin into the CS-g-pN nanogels was achieved using an incubation method. Size, morphology of nanogels, amounts of curcumin loaded to the nanogels and cellular uptake were investigated by DLS, TEM, fluorescent spectroscopy and confocal microscopy techniques, respectively. A CellTiter-Blue® cell viability assay was performed in NIH-3T3 and HeLa cells to assess the safety while MTT assay was carried out in MDA-231, Caco-2, HepG2, and HT-29 cells for determining cytotoxic effects. Results showed that CS-g-pN with 3–60% degree of modification were simply assembled into spherical nanogel particles with submicron sizes, in which curcumin was encapsulated. The thermoresponsive behavior of each CS-g-pN nanogel formulation differed due to the grafted pNIPAM length and density. The CS-g-pN nanogel formulations were non-toxic towards NIH-3T3 and HeLa cells. Each curcumin-loaded CS-g-pN nanogel formulation could be up taken into NIH-3T3 cell lines and showed the dose-dependent cytotoxicity against tested cell lines. Successful development of this curcumin-loaded nanogel will lead to advanced materials that can be functionalized and optimized for targeted therapy and controlled delivery of small molecules and/or biomolecules for biomedical applications.

Synergistic Thermoresponsive Optical Properties of a Composite Self-Healing Hydrogel

A fast (30 s) thermoresponse and rapid (30 min) self-healing were achieved by noncovalently incorporating a small fraction of poly(N-isopropylacrylamide) (PNIPAM) nanogels (≤0.18 wt %) into a benzyl methacrylate-co-octadecyl methacrylate-co-methacrylic acid (BOMA-16) polymer matrix. The PNIPAM serves as the thermoresponsive component while the BOMA-16 provides self-healing via hydrophobic associations. The PNIPAM/BOMA-16 composite showed tunable lower critical solution temperature and up to 95% more visible light modulation (ΔT) than the same concentration of PNIPAM by itself. Conversely, the PNIPAM nanogels (≤0.18 wt %) served as reinforcements and increased the storage modulus of the PNIPAM/BOMA-16 hydrogel by up to 2.7 times relative to a BOMA-16 hydrogel. Using different analytical techniques, we show that the synergistic thermoresponsive light modulation is due to a hydrophilic–hydrophobic phase transition and clustering of the PNIPAM nanogels facilitated by the BOMA-16. The synergistic optical effec...

Facile Fabrication of Composite Membranes with Dual Thermo- and pH-Responsive Characteristics.

Facile fabrication of novel functional membranes with excellent dual thermo- and pH-responsive characteristics has been achieved by simply designing dual-layer composite membranes. pH-Responsive poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers and polystyrene blended with thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) nanogels are respectively used to construct the top layer and bottom layer of composite membranes. The stretching/coiling conformation changes of the P4VP chains around the pKa (∼3.5-4.5) provide the composite membranes with extraordinary pH-responsive characteristics, and the volume phase transitions of PNIPAM nanogels at the pore/matrix interfaces in the bottom layer around the volume phase transition temperature (VPTT, ∼33 °C) provide the composite membranes with great thermoresponsive characteristics. The microstructures, permeability performances, and dual stimuli-responsive characteristics can be well tuned by adjusting the content of PNIPAM nanogels and the thickness of the PS-b-P4VP top layer. The water fluxes of the composite membranes can be changed in order of magnitude by changing the environment temperature and pH, and the dual thermo- and pH-responsive permeation performances of the composite membranes are satisfactorily reversible and reproducible. The membrane fabrication strategy in this work provides valuable guidance for further development of dual stimuli-responsive membranes or even multi stimuli-responsive membranes.