Stimuli-responsive Smart Materials Research Articles

Dual Thermo- and pH-Responsive Polymer Nanoparticle Assemblies for Potential Stimuli-Controlled Drug Delivery.

The development of stimuli-responsive drug delivery systems enables targeted delivery and environment-controlled drug release, thereby minimizing off-target effects and systemic toxicity. We prepared and studied tailor-made dual-responsive systems (thermo- and pH-) based on synthetic diblock copolymers consisting of a fully hydrophilic block of poly[N-(1,3-dihydroxypropyl)methacrylamide] (poly(DHPMA)) and a thermoresponsive block of poly[N-(2,2-dimethyl-1,3-dioxan-5-yl)methacrylamide] (poly(DHPMA-acetal)) as drug delivery and smart stimuli-responsive materials. The copolymers were designed for eventual medical application to be fully soluble in aqueous solutions at 25 °C. However, they form well-defined nanoparticles with hydrodynamic diameters of 50-800 nm when heated above the transition temperature of 27-31 °C. This temperature range is carefully tailored to align with the human body's physiological conditions. The formation of the nanoparticles and their subsequent decomposition was studied using dynamic light scattering (DLS), transmission electron microscopy (TEM), isothermal titration calorimetry (ITC), and nuclear magnetic resonance (NMR). 1H NMR studies confirmed that after approximately 20 h of incubation at pH 5, which closely mimics tumor microenvironment, approximately 40% of the acetal groups were hydrolyzed, and the thermoresponsive behavior of the copolymers was lost. This smart polymer response led to disintegration of the supramolecular structures, possibly releasing the therapeutic cargo. By tuning the transition temperature to the values relevant for medical applications, we ensure precise and effective drug release. In addition, our systems did not exhibit any cytotoxicity against any of the three cell lines. Our findings underscore the immense potential of these nanoparticles as eventual advanced drug delivery systems, especially for cancer therapy.

Being Smarter, Azobenzene-Containing Biomaterial Showing Triple Stimuli-Responsive Phase Change Property to Light, Humidity and Force at Room Temperature.

Multiple stimuli-responsiveness is an attractive property that is studied in physical chemistry and materials chemistry. While, multiple stimuli-responsive phase change in an isothermal way is rarely addressed for functional materials at room temperature. In this study, one azobenzene-containing surfactant AZO is designed for the fabrication of triple stimuli-responsive phase change biomaterial (Alg-AZO) through the electrostatic complexation with natural alginate. Thanks to the photoisomerization ability, molecular flexibility and hydrophilicity of AZO, together with the tailoring effect of alginate on AZO, Alg-AZO could perform reversible isothermal phase transition between liquid crystalline and isotropic liquid states under the stimuli of either light or humidity at room temperature. Furthermore, the humidity-induced isotropic state can also fast transit to ordered state under shear force, owing to the π-π interactions between planar trans-AZO in Alg-AZO material. With good biocompatibility, self-healing property and in vivo wound healing promoting capacity that is promoted by light, humidity and force, Alg-AZO would be suitable for working as a new smart biomaterial in biological and biomedical areas. This work provides a designing strategy for gaining multiple stimuli-responsive smart materials based on biomacromolecules, and also opening a new opportunity for gaining self-healing biomaterials capable of working in various conditions.

Dynamic Control of Chiral Recognition in Water-Soluble Naphthotubes Induced by Hydrostatic Pressure.

The dynamic control of chiral (enantiomeric) responses in chiral host-guest complexes through external stimuli is a significant challenge in modern chemistry for developing smart stimuli-responsive materials. Herein, we report the (chir)optical properties and chiral recognition behavior of water-soluble chiral naphthotubes (1) under the influence of hydrostatic pressure as an external stimulus. The hydrostatic pressure spectral profiles compared to those obtained at normal pressure revealed the dynamic behavior of 1 under hydrostatic pressure, owing to the flexible linker. In chiral recognition experiments, hydrophilic amino acids such as phenylalanine (Phe) and tryptophan (Trp) exhibited reaction volume changes (ΔV°) of -0.9 cm3 mol-1 for d-Phe, -1.2 cm3 mol-1 for l-Phe, -5.6 cm3 mol-1 for d-Trp, and -7.0 cm3 mol-1 for l-Trp, with enantioselectivity ranging from 1.2 to 1.6. In contrast, hydrophobic chiral styrene oxide (2) showed ΔV° values of 1.5 cm3 mol-1 for R-2 and 3.5 cm3 mol-1 for S- 2, with a relatively higher enantioselectivity of up to 7.6. These contrasting effects of hydrostatic pressure primarily originate from the dynamics of chiral naphthotubes.

Investigating the nonlinear dynamics of photosensitive Belousov-Zhabotinsky gels via bifurcation analyses.

Controlling the dynamics of active stimuli-responsive smart materials is essential to replicate the biomimetic functionalities at different length scales for a variety of biological systems-based applications. Photosensitive Belousov-Zhabotinsky (BZ) gels, powered by a nonlinear chemical oscillator, called a BZ reaction are one of the stimuli-responsive smart materials in demand due to their ability to continuously transduce chemical oscillations into mechanical deformations. The chemical oscillations in a BZ reaction and subsequent mechanical oscillations in photosensitive BZ gels occur due to the redox cycle of photosensitive ruthenium complex-based catalysts. In this work, our objective is to identify how the behavior of photosensitive BZ gels can be tuned and used for biomimetic applications by investigating its dynamical characteristics using bifurcation analyses. Specifically, we use the normal form approach and perform linear and nonlinear stability analyses to identify high-order bifurcations by computing higher-order Lyapunov and frequency coefficients. We revealed the existence of domains that encompass coexisting stable and unstable limit cycles (LCs), which merge to form a semi-stable LC at the limit point of cycle (LPC). Their existence shows how a slight variation in the BZ gel recipe can significantly alter its dynamics. Subsequently, we quantify the amplitude and frequency of oscillations in different domains under the effect of variation of BZ reaction formulations. We believe that the outcomes of our work serve as an efficient template for the design and control of BZ gel-based applications. The usage of a normal form and a systematic representation of nonlinear dynamics allow our framework to be extended for other nonlinear dynamical systems.

Understanding the shape-memory mechanism of thermoplastic polyurethane by investigating the phase-separated morphology: A dissipative particle dynamics study

Shape-memory polyurethanes (SMPUs) are promising materials that change shape in response to external heat. These polymers have a dual-segment structure: a hard segment for netpoint and a soft segment for molecular switch. Understanding the molecular behavior of each segment and microphase-separated morphology is crucial for comprehending the shape-memory mechanism. This study aimed to understand the shape-memory behavior by observing the phase separation of SMPU using mesoscale models based on dissipative particle dynamics (DPD) simulations. The SMPU copolymer was modeled using 4,4′-diphenylmethane diisocyanate (MDI, hard segment) and poly(ethylene oxide) (PEO, soft segment). By calculating segment solubility and repulsion parameters, we found that the hard-segment domain changes from isolated form to a lamellar and interconnected structure and eventually to a continuous form as its content increases. Combining these insights with shape-memory performance models can enhance our understanding of better SMPU design and contribute significantly to the optimization of smart stimuli-responsive materials.

Programmable Photoswitchable Microcapsules Enable Precise and Tailored Drug Delivery from Microfluidics.

The development of precision personalized medicine poses a significant need for the next generation of advanced diagnostic and therapeutic technologies, and one of the key challenges is the development of highly time-, space-, and dose-controllable drug delivery systems that respond to the complex physiopathology of patient populations. In response to this challenge, an increasing number of stimuli-responsive smart materials are integrated into biomaterial systems for precise targeted drug delivery. Among them, responsive microcapsules prepared by droplet microfluidics have received much attention. In this study, we present a UV-visible light cycling mediated photoswitchable microcapsule (PMC) with dynamic permeability-switching capability for precise and tailored drug release. The PMCs were fabricated using a programmable pulsed aerodynamic printing (PPAP) technique, encapsulating an aqueous core containing magnetic nanoparticles and the drug doxorubicin (DOX) within a poly(lactic-co-glycolic acid) (PLGA) composite shell modified by PEG-b-PSPA. Selective irradiation of PMCs with ultraviolet (UV) or visible light (Vis) allows for high-precision time-, space-, and dose-controlled release of the therapeutic agent. An experimentally validated theoretical model was developed to describe the drug release pattern, holding promise for future customized programmable drug release applications. The therapeutic efficacy and value of patternable cancer cell treatment activated by UV radiation is demonstrated by our experimental results. After in vitro transcatheter arterial chemoembolization (TACE), PMCs can be removed by external magnetic fields to mitigate potential side effects. Our findings demonstrate that PMCs have the potential to integrate embolization, on-demand drug delivery, magnetic actuation, and imaging properties, highlighting their immense potential for tailored drug delivery and embolic therapy.

Luminescent properties of multi-stimuli-responsive Ln-BPDC-Phen Lanthanide complexes

Stimuli-responsive smart luminescent materials have attracted more and more attention recently. A series of lanthanide organic complexes, [Ln2(BPDC)3(Phen)2(DMF)2]·5H2O (Ln: lanthanide = Eu, Tb, EuxTb1−x, H2BPDC = 2,2′-Bipyridine-5,5′-dicarboxylic acid, H2Phen = 1,10-phenanthroline, DMF = N,N-dimethylformamide), were synthesized and characterized to be iso-structural. The complexes demonstrate selective and significant response to Fe3+ ions, leading to fast and accurate measuring of Fe3+ ions. Interestingly, the complexes exhibit diverse luminescent response to two isomers 2, 6-pyridine dicarboxylic acid (DPA) and 3, 5-pyridine dicarboxylic acid (H2PDC). The green emission due to Tb3+ ions is enhanced by DPA upon excitation of 280 nm, which is ascribed to the absorption of DPA. Whilst it is quenched by DPA with the excitation of the ligands (339 nm). However, H2PDC quenches both the green and red emissions regardless of the excitation wavelength. The reason is that DPA provides more possibilities of the ligand exchange with the complex due to the suitable position of the carboxylic acid functional groups on the pyridine ring than H2PDC. Simultaneously, the luminescent response of the complex to DPA enables emission color tunability, which allows the complex to recognize and measure DPA/H2PDC isomers visually and easily. Moreover, the complex exhibits a wide-range (110–360 K) temperature sensing with high Sr = 3.92 %K−1 at 180 K. The multi-stimuli-response of the complexes makes them potential applicants for multi-functional sensing materials.

Prospective of functionalized graphene as shape memory and self-healing polymer: A review

Polymer matrix composites despite having potential as high-performance smart materials face challenges in various sectors including infrastructure, biomedical and automotive due to their lower strength and stiffness. The incorporation of graphene into the polymer matrix has shown significant improvement in mechanical, thermal and other material properties. Furthermore, due to certain shortcomings of graphene such as agglomeration and poor transfer of properties, functionalization of graphene has revolutionised the research field. It also exhibits futuristic applications as filler in stimuli-responsive smart materials. The prospective of functionalized graphene's potentiality as shape memory and self-healing polymers and their realistic applications in various areas have been discussed.

Brightening Blue Photoluminescence in Non-emission MOF-2 by Pressure Treatment Engineering.

As equally essential as the synthesis of new materials, manoeuvring new structure configurations can endow the brand-new functional properties to existing materials, which is also one of the core goals in the synthesis community. In this respect, pressure-induced emission (PIE) that triggers photoluminescence (PL) in non-emission materials is an emerging stimuli-responsive smart materials technology. In the PIE paradigms, harvesting bright PL at ambient conditions, however, has remained elusive. Herein, we report a remarkable PIE phenomenon in initially non-emission MOF-2, which shows bright blue-emission at 455nm under pressure. Intriguingly, the bright blue PL with an excellent photoluminescence quantum yield up to 70.4% is unprecedentedly retained to ambient conditions upon decompression from 16.2GPa. The detailed structural analyses combined with density functional theory calculations reveal that hydrogen bonding cooperativity effect elevates powerfully the rotational barrier of the linker rotor to 3.87eV/mol from initial 0.91eV/mol through pressure treatment. The downgrade rotational freedom turns on PL of MOF-2 after releasing pressure completely. This is the first case of harvesting PIE to ambient conditions. Our findings offer a new platform for the creation of promising alternatives to high-performance PL materials based on initially non-emission counterparts. This article is protected by copyright. All rights reserved.

Self-powered stimuli responsive material for dual stimulation of heat and guest molecules

Stimuli-responsive smart materials exhibit reverse chemical/physical changes in response to external stimuli and research on stimuli-responsive smart materials with self-powered properties is still uncultivated ground. Here, we report perovskite crystalline self-powered multiple stimuli-responsive materials triggered by chemical and thermal stimuli. [HMEP]PbI3·(H2O) (1; HMEP is a hydroxytris(1-methylethyl)phosphorus cation) crystallizes in a chiral space group P21 at 293 K and has the piezoelectric reaction (d33 = 10 pC/N and output voltage = 1 V) of self-powered modes, this value is larger than the value of 3 pC/N for the classical piezoelectric material ZnO. Piezoelectric materials can generate energy due to mechanical deformation, and using thermal heating to lose water, [HMEP]PbI3 (2) can be obtained. 2 crystallizes in the non-centrosymmetric space group, undergoes two reversible phase transitions at 243/255 K and 315/348 K, and shows second harmonic generation switching. Interestingly, 2 can return to the hydrated form 1 after absorbing water. This work will lay the foundation for self-powered stimuli-responsive compounds and contribute to the construction of novel organic-inorganic hybrid materials with second harmonic generation switching.

A Review of Stimuli-Responsive Smart Materials for Wearable Technology in Healthcare: Retrospective, Perspective, and Prospective.

In recent years thanks to the Internet of Things (IoT), the demand for the development of miniaturized and wearable sensors has skyrocketed. Among them, novel sensors for wearable medical devices are mostly needed. The aim of this review is to summarize the advancements in this field from current points of view, focusing on sensors embedded into textile fabrics. Indeed, they are portable, lightweight, and the best candidates for monitoring biometric parameters. The possibility of integrating chemical sensors into textiles has opened new markets in smart clothing. Many examples of these systems are represented by color-changing materials due to their capability of altering optical properties, including absorption, reflectance, and scattering, in response to different external stimuli (temperature, humidity, pH, or chemicals). With the goal of smart health monitoring, nanosized sol–gel precursors, bringing coupling agents into their chemical structure, were used to modify halochromic dyestuffs, both minimizing leaching from the treated surfaces and increasing photostability for the development of stimuli-responsive sensors. The literature about the sensing properties of functionalized halochromic azo dyestuffs applied to textile fabrics is reviewed to understand their potential for achieving remote monitoring of health parameters. Finally, challenges and future perspectives are discussed to envisage the developed strategies for the next generation of functionalized halochromic dyestuffs with biocompatible and real-time stimuli-responsive capabilities.

Stimuli-Responsive Crystalline Smart Materials: From Rational Design and Fabrication to Applications.

Stimuli-responsive smart materials that can undergo reversible chemical/physical changes under external stimuli such as mechanical stress, heat, light, gas, electricity, and pH, are currently attracting increasing attention in the fields of sensors, actuators, optoelectronic devices, information storage, medical applications, and so forth. The current smart materials mostly concentrate on polymers, carbon materials, crystalline liquids, and hydrogels, which have no or low structural order (i.e., the responsive groups/moieties are disorderly in the structures), inevitably introducing deficiencies such as a relatively low response speeds, energy transformation inefficiencies, and unclear structure-property relationships. Consequently, crystalline materials with well-defined and regular molecular arrays can offer a new opportunity to create novel smart materials with improved stimuli-responsive performance. Crystalline materials include framework materials (e.g., metal-organic frameworks, MOFs; covalent organic frameworks, COFs) and molecular crystals (e.g., organic molecules and molecular cages), which have obvious advantages as smart materials compared to amorphous materials. For example, responsive groups/moieties can be uniformly installed in the skeleton of the crystal materials to form ordered molecular arrays, making energy transfer between external-stimulus signals and responsive sites much faster and more efficiently. Besides that, the well-defined structures facilitate in situ characterization of their structural transformation at the molecular level by means of various techniques and high-tech equipment such as in situ spectra and single-crystal/powder X-ray diffraction, thus benefiting the investigation and understanding of the mechanism behind the stimuli-responsive behaviors and structure-property relationships. Nevertheless, some unsolved challenges remain for crystalline smart materials (CSMs), hampering the fabrication of smart material systems for practical applications. For instance, as the materials' crystallinity increases, their processability and mechanical properties usually decrease, unavoidably hindering their practical application. Moreover, crystalline smart materials mostly exist as micro/nanosized powders, which are difficult to make stimuli-responsive on the macroscale. Thus, developing strategies that can balance the materials' crystallinity and processability and establishing macroscale smart material systems are of great significance for practical applications.In this Account, we mainly summarize the recent research progress achieved by our groups, including (i) the rational design and fabrication of new stimuli-responsive crystalline smart materials, including molecular crystals and framework materials, and an in-depth investigation of their response mechanism and structure-property relationship and (ii) creating chemical/physical modification strategies to improve the processability and mechanical properties for crystalline materials and establishing macroscale smart systems for practical applications. Overall, this Account summarizes the state-of-the-art progress of stimuli-responsive crystalline smart materials and points out the existing challenges and future development directions in the field.

Erasable glass-stabilized perovskite quantum dots for NIR-laser-stimuli-responsive optical security

Stimuli-responsive smart luminescent materials capable of dynamic color emission with distinct spectral profile/intensity are highly desirable for anti-counterfeiting applications. Here, we report the dynamic manipulation of photoluminescence from metal halide CsPbX 3 (X = Br, I) perovskite quantum dots (PeQDs) inside a glass medium by tuning local temperature fields in real time in combination with the efficient photothermal material CsYb 2 F 7 @glass. Benefiting from the effective protection of the inorganic glass matrix and low exciton binding energy of PeQDs, it is feasible to realize stable and reversible ON/OFF full-spectral emissions of PeQDs upon commercial 980 nm laser stimulation. The dynamic combination of downshifting PeQDs and upconverting lanthanide-doped CsYb 2 F 7 can be elaborately designed to produce a series of erasable photochromic anti-counterfeiting patterns and multi-dimensional optical encodings. • An approach to dynamically manipulate PL of CsPbX 3 QDs inside glass is developed • Laser-induced Ln 3+ photothermal effect is used to lighten/quench PL of CsPbX 3 @glass • Erasable photochromic anti-counterfeiting and optical encodings are demonstrated Wang et al. demonstrate the dynamic manipulation of erasable emissions from CsPbX 3 perovskite quantum dots (PeQDs) inside a glass medium by tuning local temperature fields in real time with the help of the efficient photothermal material CsYb 2 F 7 . This controllable combination of rare-earth/PeQDs may enable their practical application in high-level optical security.

Recent Developments in Stimuli Responsive Smart Materials and Applications: An Overview

The term “smart materials” can be used to refer a wide variety of different kinds of substances. One capacity that is shared by all of them is the capability to radically alter one or more aspects while operating inside carefully controlled conditions. The age of intelligent materials is arrived, and we are living in it right now. An older definition of smart material described it as a substance that responds swiftly to the environment in which it is located. It has been argued that the word “smart material” now refers to any substance that is capable of detecting, transmitting, or processing a stimulus in order to produce a beneficial effect. This idea has been put forward as a possible expansion of the original meaning of the term. The purpose of this research is to define and categorize different types of intelligent materials. Uses of smart materials are being contemplated in a wide variety of domains, spanning from the realm of technology to that of the modern environment.

Advances in Organic Ionic Materials Based on Ionic Liquids and Polymers

Abstract Ionics has emerged as an important scientific area for realizing the key materials necessary for the development of advanced electrochemical devices that would support a sustainable society. In this paper, new organic ion-conducting materials such as ionic liquids and polymer electrolytes are the research focus, as conventional aqueous and organic electrolyte solutions have several disadvantages that prove to be a bottleneck for making a breakthrough in electrochemical materials and devices. A detailed investigation of the ion dynamics in these materials and their interfaces with electrodes was performed, and significant contribution was made to establish the field of organic ionics. Furthermore, stimuli-responsive smart materials based on ionic liquids and polymers have been proposed, and new materials distinguished by advantageous features have been realized. The relevant studies are reviewed in this paper.

Electrospun Sericin/PNIPAM-Based Nano-Modified Cotton Fabric with Multi-Function Responsiveness

There is a significant interest in developing environmentally responsive or stimuli-responsive smart materials. The purpose of this study was to investigate multi-function responsive cotton fabrics with surface modification on the nanoscale. Three technologies including electrospinning technology, interpenetrating polymer network technology, and cross-linking technology were applied to prepare the multi-function sericin/poly(N-isopropylacrylamide)/Poly(ethylene oxide) nanofibers, which were then grafted onto the surfaces of cotton textiles to endow the cotton textiles with outstanding stimuli-responsive functionalities. The multi-function responsive properties were evaluated via SEM, DSC, the pH-responsive swelling behavior test and contact angle measurements. The results demonstrate that with this method, multi-function responsive, including thermo- and pH-responsiveness, cotton fabrics were fast formed, and the stimuli-responsiveness of the materials was well controlled. In addition, the antimicrobial testing reveals efficient activity of cotton fabrics with the sericin/PNIPAM/PEO nanofiber treatments against Gram-positive bacteria and Gram-negative bacteria such as Staphylococcus aureus and Escherichia coli. The research shows that the presented strategy demonstrated the great potential of multi-function responsive cotton fabrics fabricated using our method.

Color regulation for dual-states of electrochromic polymer accompanied with light induced coloration effect

With the developing demand for the smart stimuli-responsive materials, the functional conjugated polymers are appealing for the electrochromic materials, due to their adjustable structure, rapid switching time and facile processability. Series of innovative conjugated electrochromic polymers consisting of triphenylamine or phenothiazine group have been designed and synthesized. Other than the conventional electrochromic polymers, our designed polymers can control colors of both reduction and oxidation states with applied external potential. With incorporation of side anode electrochromic group, the polymers bearing triphenylamine group can achieve grey-blue color at oxidation states and those containing phenothiazine group can present dark purple color at their oxidation states. With further modification of polymer backbone, the reduction colors of electrochromic polymers can be regulated as well. Therefore, the effective combination of anode and cathode electrochromic materials in one can realize color regulation for the dual-states as expected. Additionally, the polymers bearing triphenylamine group can further achieve light induced coloration effect as the triphenylamine group can act as light-induced energy source to drive the reduction of polymer backbone. Therefore, the design and effects of these polymers can broaden application range of electrochromic polymers and provide new strategies for energy saving material design.

Effect of aromatic acid on the rheological behaviors and microstructural mechanism of wormlike micelles in betaine surfactant

The rheology and microstructural behaviors of viscoelastic surfactant solutions induced by different organic acids are fascinating. However, the viscosity and viscoelasticity behavior of some surfactants such as oleyl amidopropyl betaine (OAPB) surfactant is very poor even at high concentrations. To improve these properties at low concentrations, a system of OAPB and phthalic acid (OPA) at a mass ratio of 3:2 has been developed. The rheological behaviors and microstructural aggregations of the OAPB/OPA system were measured by rheometer, transmission electron microscopy (Cryo-TEM), and dynamic light scattering (DLS). The experimental results showed that the addition of OPA significantly increases the viscoelasticity and viscosity properties of the OAPB viscoelastic micelle solutions at 25°C. The improvements of these properties are attributed to the formation of a micellar network due to the addition of OPA. The rheology and micellar properties were found to transform a transparent viscous water like a fluid at pH 7 to a viscoelastic fluid at pH 2.9. The zero-shear viscosity and relaxation times declined exponentially with an increase of temperature indicating a reduction in the average micellar lengths. The properties changes were attributed to the strength of electrostatic attractions, hydrophobic effects, and hydrogen bonding between OAPB and OPA molecules. Since the current system can be easily tuned by pH for at least 3 circles without deterioration of its properties, the system unlocks the significant prospect for designing stimuli-responsive smart materials for various industrial applications.

Nucleation Points: The Forgotten Parameter in the Synthesis of Hydrogel-Coated Gold Nanoparticles.

The implementation of gold-hydrogel core-shell nanomaterials in novel light-driven technologies requires the development of well-controlled and scalable synthesis protocols with precisely tunable properties. Herein, new insights are presented concerning the importance of using the concentration of gold cores as a control parameter in the seeded precipitation polymerization process to modulate—regardless of core size—relevant fabrication parameters such as encapsulation yield, particle size and shrinkage capacity. Controlling the number of nucleation points results in the facile tuning of the encapsulation process, with yields reaching 99% of gold cores even when using different core sizes at a given particle concentration. This demonstration is extended to the encapsulation of bimodal gold core mixtures with equally precise control on the encapsulation yield, suggesting that this principle could be extended to encapsulating cores composed of other materials. These findings could have a significant impact on the development of stimuli-responsive smart materials.

Morphologies of a spherical bimodal polyelectrolyte brush induced by polydispersity and solvent selectivity* *Project supported by the Fundamental Research Funds for the Central Universities of China (Grant No. 3122020080).

It is commonly realized that polydispersity may significantly affect the surface modification properties of polymer brush systems. In light of this, we systematically study morphologies of bidisperse polyelectrolyte brush grafted onto a spherical nanocolloid in the presence of trivalent counterions using molecular dynamics simulations. Via varying polydispersity, grafting density, and solvent selectivity, the effects of electrostatic correlation and excluded volume are focused, and rich phase behaviors of binary mixed polyelectrolyte brush are predicted, including a variety of pinned-patch morphologies at low grafting density and micelle-like structures at high grafting density. To pinpoint the mechanism of surface structure formation, the shape factor of two species of polyelectrolyte chains and the pair correlation function between monomers from different polyelectrolyte ligands are analyzed carefully. Also, electrostatic correlations, manifested as the bridging through trivalent counterions, are examined by identifying four states of trivalent counterions. Our simulation results may be useful for designing smart stimuli-responsive materials based on mixed polyelectrolyte coated surfaces.