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Laser-driven structural transformations in dextran- <i>graft</i> -PNIPAM copolymer/Au nanoparticles hybrid nanosystem: the role of plasmon heating and attractive optical forces
摘要： Laser induced structural transformations in a dextran grafted-poly(N-isopropylacrylamide) copolymer/Au nanoparticles (D-g-PNIPAM/AuNPs) hybrid nanosystem in water have been observed. The laser induced local plasmonic heating of Au NPs leads to Lower Critical Solution Temperature (LCST) phase transition in D-g-PNIPAM/AuNPs macromolecules accompanied by their shrinking and aggregation. The hysteresis non-reversible character of the structural transformation in D-g-PNIPAM/AuNPs system has been observed at the decrease of laser intensity, i.e. the aggregates remains in solution after the turn-off the laser illumination. This is an essential difference comparing to the case of usual heating–cooling cycles when there is no formation of aggregates and structural transformations are reversible. Such a fundamental difference has been rationalized as the result of action of attractive optical forces arising due to the excitation of surface plasmons in Au NPs. The attractive plasmonic forces facilitate the formation of the aggregates and counteract their destruction. The laser induced structural transformations have been found to be very sensitive to matching conditions of the resonance of the laser light with surface plasmon resonance proving the plasmonic nature of observed phenomena.
关键词： Plasmon heating,Attractive optical forces,LCST phase transition,Au nanoparticles,Laser induced structural transformations,Dextran-graft-PNIPAM copolymer
更新于2025-11-19 16:56:42
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Preparation of a star-shaped copolymer with porphyrin core and four PNIPAM-b-POEGMA arms for photodynamic therapy
摘要： A series of thermosensitive star-shaped copolymers THPP-(PNIPAM-b-POEGMA)4 with 5, 10, 15,20-tetrakis-(4-hydroxyphenyl)-21H,23H-porphyrin (THPP) core and four poly(N-isopropylacrylamide)-b-poly(oligo(ethylene glycol) mono methyl ether methacrylate) (PNIPAM-b-POEGMA) arms were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The low critical solution temperatures (LCSTs) of THPP-(PNIPAM-b-POEGMA)4 with different molecular weights were 37.5 °C, 39.9 °C and 41.9 °C respectively, which depending on the hydrophilic POEGMA contents of copolymers. The micellar structures of copolymers could be formed above the LCSTs. The MTT study indicated that THPP-(PNIPAM-b-POEGMA)4 and THPP showed no significant cytotoxicity toward HeLa cells and L929 cells. And THPP-(PNIPAM-b-POEGMA)4 under light irradiation showed photodynamic activity which photo-toxicity toward HeLa cells was stronger than THPP.
关键词： Porphyrin,Thermosensitivity,Reversible addition-fragmentation chain transfer (RAFT),THPP-(PNIPAM-b-POEGMA)4,Photodynamic therapy
更新于2025-09-23 15:22:29
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Controlling the shape of 3D microstructures by temperature and light
摘要： Stimuli-responsive microstructures are critical to create adaptable systems in soft robotics and biosciences. For such applications, the materials must be compatible with aqueous environments and enable the manufacturing of three-dimensional structures. Poly(N-isopropylacrylamide) (pNIPAM) is a well-established polymer, exhibiting a substantial response to changes in temperature close to its lower critical solution temperature. To create complex actuation patterns, materials that react differently with respect to a stimulus are required. Here, we introduce functional three-dimensional hetero-microstructures based on pNIPAM. By variation of the local exposure dose in three-dimensional laser lithography, we demonstrate that the material parameters can be altered on demand in a single resist formulation. We explore this concept for sophisticated three-dimensional architectures with large-amplitude and complex responses. The experimental results are consistent with numerical calculations, able to predict the actuation response. Furthermore, a spatially controlled response is achieved by inducing a local temperature increase by two-photon absorption of focused light.
关键词： light-induced actuation,pNIPAM,temperature response,stimuli-responsive materials,gray-tone lithography,hetero-microstructures,laser lithography,3D microstructures
更新于2025-09-23 15:22:29
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[ACS Symposium Series] Gels and Other Soft Amorphous Solids Volume 1296 || Probe Diffusion Dynamic Light Scattering of Polymer solutions and Gels
摘要： Probe diffusion dynamic light scattering technique is a powerful to investigate the dynamics of polymer chains in polymer solutions and gels. Not only the local dynamics and/or local viscosity but also the gel point and the post-gel dynamics can be investigated. In this chapter, we discuss (1) a conventional probe diffusion of radical polymerization of poly(N-isopropylacrylamide) (PNIPAM) aqueous system, (2) an in-situ isorefractive probe diffusion of tetra-arm poly(ethylene glycol) (Tetra-PEG) undergoing sol-gel transition via cross-end-coupling, and (3) of PNIPAM radical polymerization. It is demonstrated that the gel point is determined as a function of the reaction conversion, which is a more universal measure than the reaction time. The post-gel dynamics explored by the probe particles illuminates the local dynamics in a “pool” of the sol phase surrounded by a gel network. Furthermore, comparison in dynamics is made between well-controlled uniform networks (Tetra-PEG gels) and randomly cross-linked more heterogeneous networks (PNIPAM gels) the probe size from the viewpoints of dependence and scattering angle dependence.
关键词： gel point,Tetra-PEG,post-gel dynamics,Probe diffusion,PNIPAM,gels,polymer solutions,dynamic light scattering
更新于2025-09-23 15:21:21
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Novel phthalocyanine-based micelles/PNIPAM composite hydrogels: spatial/temporal-controlled drug release triggered by NIR laser irradiation
摘要： Near-infrared (NIR) light-responsive hydrogels hold significant potential for biomedical application, especially in remote-controlled release of anticancer drugs. Herein we report a novel NIR light responsive composite hydrogel system that undergoes structural changes to realize drug delivery and precise release, which are constructed by poly (N-isopropylacrylamide) network and photothermal agent 4OCSPC/F127 micelles.
关键词： PNIPAM,NIR light-responsive hydrogels,4OCSPC/F127 micelles,drug delivery,photothermal agent
更新于2025-09-23 15:21:01
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Plasmonics of Au/Polymer Core/Shell Nanocomposites for Thermoresponsive Hybrid Metasurfaces
摘要： We investigate the temperature-dependent optical response of ordered lattices of non-interacting gold-core/poly(N-isopropylacrylamide)-shell nanoparticles (NPs), a system with proven photothermal and sensing capabilities. For the first time on this system, we exploited in situ Spectroscopic Ellipsometry (SE) to determine the complex, temperature-dependent optical properties of the lattice, a key piece of information which, however, is often overlooked. In doing so, we take full advantage of large-scale colloidal self-assembly, which makes NP lattices accessible to conventional SE. A quantitative interpretation of the SE data is obtained through an effective model based on the actual characteristics of the NPs and their dielectric environment. The model allows to estimate temperature-dependent morphological parameters, such as the distance between the gold cores and the substrate, also yielding the complex permittivity of the plasmonic NP lattice. Thus, by combining the high sensitivity of SE with proper modelling, we provide a comprehensive characterization of thermoresponsive NP lattices. The approach proposed here is instrumental to the analysis and design of functional hybrid metasurfaces with plasmonic functionalities, including particle-to-film coupled systems.
关键词： spectroscopic ellipsometry,PNIPAM,localized surface plasmon resonance,complex permittivity,core-shell particles
更新于2025-09-19 17:13:59
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Two-Stage Collapse of PNIPAM Brushes: Viscoelastic Changes Revealed by an Interferometric Laser Technique
摘要： Many temperature-responsive polymers exhibit a single-phase transition at the lower critical solution temperature (LCST). One exception is poly(N-isopropylacryamide) (PNIPAM). PNIPAM brush layers (51 ± 3 nm thick) that are end-grafted onto glass beads collapse in two stages. The viscoelastic changes of a PNIPAM brush layers were investigated with an interferometric laser method at different temperatures. This method is able to measure the two-stage collapse of beads coated with a polymer brush layer. When these beads are situated close to a hydrophilic glass surface, they exhibit Brownian motion. As this Brownian motion changes with temperature, it reveals the collapse of the polymer layer. The characteristic spectrum of the Brownian motion of beads are modelled by a damped harmonic oscillator, where the polymer layer acts as both spring and damping. The change of the Brownian motion spectrum with temperature indicates two transitions of the PNIPAM brush layer, one at 36 °C and one at 46 °C. We attribute the first transition to the LCST volume collapse of PNIPAM. Here, changes of the density and viscosity of the brush dominate. The second transition is dominated by a stiffening of the brush layer.
关键词： PNIPAM,viscoelastic changes,interferometric laser technique,brush layers,temperature-responsive polymers,two-stage collapse
更新于2025-09-19 17:13:59
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Machine learning based temperature prediction of poly( <i>N</i> -isopropylacrylamide)-capped plasmonic nanoparticle solutions
摘要： The temperature-dependent optical properties of gold nanoparticles that are capped with the thermo-sensitive polymer: ‘poly(N-isopropylacrylamide)’ (PNIPAM), have been studied extensively for several years. Also, their suitability to function as nanoscopic thermometers for bio-sensing applications has been suggested numerous times. In an attempt to establish this, many have studied the temperature-dependent optical resonance characteristics of these particles; however, developing a simple mathematical relationship between the optical measurements and the solution temperature remains an open challenge. In this paper, we attempt to systematically address this problem using machine learning techniques to quickly and accurately predict the solution-temperature, based on spectroscopic data. Our emphasis is on establishing a simple and practically useful solution to this problem. Our dataset comprises spectroscopic absorption data from both nanorods and nanobipyramids capped with PNIPAM, measured at discretely varied and pre-set temperature states. Specific regions of the spectroscopic data are selected as features for prediction using random forest (RF), gradient boosting (GB) and adaptive boosting (AB) regression techniques. Our prediction results indicate that RF and GB techniques can be used successfully to predict solution temperatures instantly to within 1 1C of accuracy.
关键词： PNIPAM,spectroscopic data,temperature prediction,adaptive boosting,machine learning,random forest,gradient boosting,gold nanoparticles
更新于2025-09-16 10:30:52
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Growing In‐Plane Multiplex Plasmonic Arrays for Synergistic Enhanced Photocurrent Response
摘要： A complete control of the localized surface plasmon resonance (LSPR) properties of different types of metal nanoparticles (size, shape, or composition) in a device by facile techniques with high throughput is crucial to intensively study and apply the LSPR effects to improve device performance. Here, a versatile approach is presented to fabricate macroscopic and in-plane multiplex arrays of plasmonic nanoparticles with well-defined particle size or composition allocation. The polymer layer (poly(N-isopropylacrylamide), PNIPAM) spin-coated on the surface of the substrate is applied as a protective layer to control the growth of the Au nanoparticles in a dip-coating procedure. The relative contribution of LSPR of each particle type can be controlled by selectively adjusting the particle size or composition at the desired position of multiplex arrays on the same substrate. A synergistic enhanced photocurrent response is observed in the metal–semiconductor system, which is attributed to broadened LSPR enhancement of multiplex composition (Au and Au@Ag) structures from the same substrate. The fabrication procedure presented in this study is highly repeatable and feasible for preparing ordered multiplex nanostructures on the same substrate. Furthermore, this method provides a cost-effective and versatile platform for design of multiplex plasmonic nanostructures in sensing, solar energy conversion, and optical processing applications.
关键词： PNIPAM,plasmonic enhancement,Au@Ag,Au,photocurrent response,tunable absorption wavelength
更新于2025-09-12 10:27:22