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* E-mail: zhangy@snnu.edu.cn; Tel.: 0086-029-85300932; Fax: 0086-029-85307609 Received November 10, 2009; revised August 8, 2010; accepted September 20, 2010. Project supported by the National Natural Sciences Foundation of China (No. 20373039), and the Natural Science Foundation of Shaanxi Province of

China (No. 2007E106)

Chin. J. Chem. 2011, 29, 33—40 © 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 33

Preparation of CuS-P(NIPAM-co-MAA) Hybrid Microgels with Controlled Surface Structures

Zhang, Ying*(张颖) Liu, Huijin(刘慧瑾) Fang, Yu(房喻)

Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, School of Chemistry and Materi-als Science, Shaanxi Normal University, Xi'an, Shaanxi 710062, China

Copper sulfide-poly(isopropylacrylamide-co-methacrylic acid) [CuS-P(NIPAM-co-MAA)] hybrid microgels with patterned surface structures have been synthesized by means of the polymer microgel template technique. The results showed that the surface morphology of the hybrid microgels could be regulated by controlling the decompo-sition of thioacetamide (TAA) in an acidic medium. The rate of precipitation and the amount of metal sulfide sig-nificantly affect the surface structures of the hybrid microgels.

Keywords polymer microgels, templates, metal sulfides, organic-inorganic hybrid composite

Introduction

Over the past several decades, polymer microgels have attracted much attention both in fundamental stud-ies of colloid science and in extensive applied fields. As is well known, polymer microgels have rapidly found important applications in materials science areas owing to their crosslinked structures with three-dimensional network topologies and their ability to undergo large swelling-deswelling transitions in response to external stimuli (e.g., temperature, pH, ionic strength, electric and magnetic fields, etc.).1-3 Among the vast number of applications, the use of polymer microgels as microre-actors, microcontainers, or templates for the synthesis, storage, and transportation of nanostructured inorganic materials has been extensively explored in recent years. Most reports have been mainly focused on the introduc-tion of different inorganic materials in the form of nanoparticles into the porous microgels structures or the template-based synthesis of nanoparticles in microgels hosts.4-8

With regard to the reaction route for the preparation of microgels-based inorganic composite materials, three different approaches are commonly used. (1) The first method involves the in situ synthesis of inorganic nanoparticles inside the network or on the surface of polymer microgels by means of deposition, reduction, or oxidation processes of the corresponding inorganic cations. In this case, polymer microgels often act as mi-croreactors,9-12 templates,13-20 or stabilizers21-23 for the preparation of inorganic nanoparticles. (2) The second alternative for the preparation of inorganic nanoparti-cle-based polymer microgels is to generate inorganic- organic composites by a physical entrapment method

using the stimuli-responsive properties of polymer mi-crogels. Usually, pre-formed inorganic nanoparticles are absorbed on the surface or diffuse into the interior of microgels in response to external stimuli such as tem-perature, pH, or ionic strength. The porous structures of the microgels may then be tuned through changes in the external environment, such that the inorganic nanoparti-cles are controllably taken-up or released in the network of the polymer microgels.24-26 (3) The third method is to synthesize hybrid microgels by encapsulation of pre-formed inorganic nanoparticles inside polymer mi-crogels during the polymerization of monomers. In par-ticular, polymerization has been conducted using func-tional initiators to give a polymer microgel as a solid matrix, or nanoparticles have been attached to the polymer chains by covalent bonds.27-30

No matter which one of the preparation methods is employed, the polymer microgels often have responses to external stimuli. Responses to external stimuli result from the interactions between the microgels’ own spe-cies and others, as well as environmental changes. Naturally, the resulting inorganic-microgel composites display the stimuli-responsive properties derived from the microgels. In fact, the combing of function of the inorganic-microgel materials is mainly related to mi-crogel’s environmental responses. In turn, inorganic components introduced in the microgels also affect the stimuli-responsive ability of the polymer microgels. At the same time, the physicochemical properties of the inorganic components also can be changed in case of the microgels’ environmental responses. The properties of microgel-based composite materials are dominantly derived from the interactions mentioned above. Gener-

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ally, one of results caused by the interactions leads to the change of the network structure of microgels. For nanosized microgels, the network change of microgels is scarcely observed by SEM analysis due to its limita-tion of resolution. However, this change can be obvi-ously indicated for microgels with the range of micron size. In recent years, our research group has succeeded in preparing various inorganic-polymer composite mi-crospheres with fancy surface structures, which has been achieved through the guidance and confinement effect of polymer microgels on the deposition of inor-ganics, such as metal sulfides, metals, insoluble salts, and oxides.31-36 The results showed that the formation of varied surface structures is directly related to the defor-mation of network structure of the used microgel tem-plate. Moreover, it has been found that the surface structures of the composite microspheres may be tai-lored to some extent by varying the chemical composi-tion of the polymer microgels, or/and by modulating the amount and the type of inorganic compound used. It was noted that our previous works have been mainly focused on the preparation of the various hybrid mi-crogels containing metal sulfide with the varied novel surface patterns.31-33 The mechanism on formation of metal sulfide-microgel composites with the surface morphology is rarely systematically concerned. The main purpose of the present study is to investigate the formation mechanism of the surface structures, taking metal sulfide-polymer hybrid microgels as an example. We prepared CuS-P(NIPAM-co-MAA) hybrid mi-crogels by incorporating Cu2 ＋ into the interior of swelling P(NIPAM-co-MAA) microgels and then slowly introduced H2S gas by the decomposition of thioacetamide (TAA) in an acidic medium. In this case, the deposition rate of CuS is mostly controlled by the formation rate of H2S gas, which is determined by the initial concentration of TAA. Thus, CuS is deposited within the swollen porous network of the microgel tem-plate, leading to the formation of hybrid microspheres with patterned surface structures during a simple wash-ing and air-drying process. Moreover, the surface mor-phologies of the prepared hybrid microgels are modu-lated by the formation rate and the amount of CuS within the framework structure of the polymer microgel used. Based on the above results, the formation mecha-nism of the CuS-polymer microgel composites with the varied surface patterns was proposed.

Experimental

Materials

N-Isopropylacrylamide (NIPAM) was purified by recrystallization in mixture of hexane and benzene (1∶2 in volume ratio). Methacrylic acid (MAA) was puri-fied by distillation under reduced pressure prior to polymerization. The initiator (ammonium persulfate, APS), the crosslinking agent (N,N'-methylenebisacryl- amide, MBA), the promoter agent (N,N,N',N'-tetrame-

thylethylenediamine, TMEDA), n-heptane, acetone, copper acetate [Cu(Ac)2], thioacetamide (TAA), and hydrochloric acid (HCl) were of analytical grade. Sor-bitan monooleate (Span-80) and polyoxyethylene sorbi-tan (Tween-80) were of chemical grade. Water used in the experiment was doubly distilled.

Preparation of P(NIPAM-co-MAA) microgels

The P(NIPAM-co-MAA) microgels were prepared in the same way as reported previously.31,32 Briefly, a 250 mL three-neck flask equipped with a mechanical stirrer, a nitrogen inlet and a Hirsch funnel, 70 mL of n-heptane and 0.60 g of mixture surfactant formed by Span-80 and Tween-80 (5∶1 in mass ratio) was added. The mixture was stirred under nitrogen purging until the surfactants were uniformly dispersed at 28 ℃. At the same time, 1.20 g of NIPAM and MAA (20%, mass fraction), 0.06 g of MBA, 1 mL of APS solution (216 g/L in aqueous phase) were dissolved into 6 mL of dou-ble distilled water. Then, the above solution was added into flask and the new mixture was stirred continuously under a nitrogen atmosphere. The polymerization reac-tion was initiated by adding of 1 mL of promoter, TMEDA solution (50 g/L) and conducted under stirring (380 r/min) at 28 ℃ for 3 h. The P(NIPAM-co-MAA) microgels thus formed were collected by filtration and washed alternatively with double distilled water and acetone several times to remove the unreacted monomer and other impurities, and finally dried at room tempera-ture.

Preparation of CuS-P(NIPAM-co-MAA) hybrid mi-crogels

In a typical synthesis, 0.10 g of P(NIPAM-co-MAA) dried microgels was fully swollen in a certain volume of 0.30 mol/L Cu(Ac)2 solution overnight. Then the mi-crogels containing Cu2＋ were directly added to an in-verse system consisting of 50 mL n-heptane and 0.17 g Span-80. The resulting system containing Cu2 ＋ - P(NIPAM-co-MAA) microgels was stirred by using an electromagnetic stirrer for 50 min at room temperature. Thereafter, the dispersed Cu2 ＋ -P(NIPAM-co-MAA)

microgels system and the H2S gas source, 30 mL of 0.53 mol/L TAA acidic aqueous solution (0.60 mol/L of HCl, pH＝2) were freshly prepared and dividually placed in three small beakers, and then rapidly transferred to an in-house constructed closed reaction vessel. The inverse system was stirred for a further 20 h at a constant tem-perature of 30 ℃. Finally, the black CuS-P(NIPAM- co-MAA) hybrid microgels were collected, washed al-ternately with doubly distilled water and acetone several times, and dried at room temperature. Other CuS- P(NIPAM-co-MAA) composites with different initial TAA dosage and initial concentration of Cu(Ac)2 were prepared by employing the same procedures.

The typical procedure of frozen-dried samples was as follows: the dried-state CuS-P(NIPAM-co-MAA) composite microspheres and P(NIPAM-co-MAA) mi-

Preparation of CuS-P(NIPAM-co-MAA) Hybrid Microgels

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crogels were fully swollen by immersion in doubly dis-tilled water overnight. The swollen microspheres were then rapidly frozen with liquid nitrogen and freeze-dried for 12 h.

Characterization

The structure and morphology of the CuS-P(NIPAM-co-MAA) hybrid microgels and pure P(NIPAM-co-MAA) polymer microgels were charac-terized by a Philips Quanta-200 scanning electron mi-croscopy (SEM), operated at an accelerating voltage of 20 kV. The SEM samples were prepared by vacuum sputtering of Au onto the samples at ambient tempera-ture. The elemental compositions of the composite mi-crospheres were measured by means of an X-ray en-ergy-dispersive spectroscopy (EDS) attached to the scanning electron microscope. X-ray powder diffraction (XRD) analysis was carried out by using a Japan Rigaku D/max-III X-ray diffractometer with Cu Kα radiation at 35 kV and 40 mA. A scan rate of 0.02 (°)/s was applied to record the pattern in the 2θ range of 10°—70°. Thermo-gravimetric analyses (TGA) were performed using a Perkin-Elmer TGA-7 instrument. The measure-ments were conducted at a heating rate of 10 ℃/min under N2 atmosphere. The microspheres used as sample for TGA were dried at 50 ℃ for 12 h before measur-ing.

Results and discussion

Characterization of CuS-P(NIPAM-co-MAA) hybrid microgels

Figure 1 shows the typical SEM images of CuS-P(NIPAM-co-MAA) hybrid microgels (reaction conditions: initial copper ion concentration [Cu]0＝0.30 mol/L, initial thioacetamide concentration [TAA]0＝

0.53 mol/L). The CuS-P(NIPAM-co-MAA) hybrid mi-crogels clearly exhibit regular and spherical morpholo-gies (Figure 1a) and are not aggregated (see the Sup-porting Information). As expected, the average diameter of the microspheres was about 60 µm, equal to that of the templates used. Compared with the pure P(NIPAM-co-MAA) microgel template (see the Sup-porting Information), the surface morphologies of the CuS-P(NIPAM-co-MAA) hybrid microgels display typical wrinkled patterns with fine textured structures (Figure 1b).

In order to confirm the chemical composition of the hybrid microgel surfaces, EDS analysis of the CuS-P(NIPAM-co-MAA) composite microspheres was performed. The results revealed that the elements C, O, N, Cu, and S were present on the surface of the hybrid microgels, and also confirmed that the as-prepared ma-terials were indeed inorganic-organic composites. The Cu to S elemental ratio estimated from the EDS results was nearly 1 (Figure 2). This result is in good agree-ment with the stoichiometric molar ratio of CuS. The EDS results were further supported by XRD measure-

Figure 1 Representative SEM images of CuS-P(NIPAM-co- MAA) hybrid microgels (a) and its high magnification image (b). [Cu2＋]0＝0.30 mol/L, [TAA]0＝0.53 mol/L.

Figure 2 EDS spectrum of CuS-P(NIPAM-co-MAA) hybrid microgels.

ment (Figure 3). The XRD patterns of the CuS- P(NIPAM-co-MAA) composites reveal that some dif-fraction peaks (Figure 3a) can be indexed to hexagonal covellite CuS (JCPDS Card No. 06-0464), while the broad peak at around 21° may be assigned to amorphous P(NIPAM-co-MAA) (Figure 3b). The above results demonstrated that crystalline CuS is characterized by three peaks corresponding to the diffractions of the (102), (103), and (110) faces of the crystals. Actually, only some of the diffraction peaks can be observed due to the presence of the broad structureless bands of the template polymer.

Figure 4 shows TG curves of CuS-P(NIPAM-co- MAA) hybrid microgels and pure P(NIPAM-co-MAA) microgels, respectively. In both cases, the weight loss stage below 300 ℃ is attributed to the evaporation of physically absorbed water and residual solvent from the samples. The major weight losses took place at 320 ℃, corresponding to pyrolysis of the polymer P(NIPAM-

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Figure 3 XRD patterns of CuS-P(NIPAM-co-MAA) hybrid microgels (a) and P(NIPAM-co-MAA) microgels (b).

Figure 4 TG curves of CuS-P(NIPAM-co-MAA) hybrid mi-crogels (a) and P(NIPAM-co-MAA) microgels (b).

co-MAA). Furthermore, it should be noted that the ma-jor weight loss ended at around 380 ℃ for CuS- P(NIPAM-co-MAA) hybrid microgels (Figure 4a), and at around 437 ℃ for P(NIPAM-co-MAA) microgels (Figure 4b). These results showed that the presence of CuS within the network structure of the polymer might enhance the degradation of the polymer microgel tem-plate, indicating that CuS nanoparticles could accelerate pyrolysis of P(NIPAM-co-MAA). This phenomenon is probably related to the finding that CuS in nano size could enhance the combustion of the polymer.37

Based on the above results, the slow diffusion of H2S gas through the water/oil interface of swollen mi-crogels containing Cu2＋ ions resulted in the gradual formation of CuS particles within the porous network of the polymer microgel used. The distribution of CuS in situ formed into hybrid microgels is attributed to the dual influences of the guidance and confinement de-rived from the polymer microgel template. It is easy to understand that the framework of deposited CuS be-come rigid, whereas the framework without CuS keeps flexibility. The difference in rigidity of the frameworks in the hybrid microgels is responsible to the surface morphology of the hybrid microgels. Naturally, all fac-tors affected the deposition of CuS would influence on the surface morphology of the composite microgels. In

fact, it has been found that the surface morphologies of the composite microgels are dependent upon the various factors, such as the rate of the deposition reaction and the amount of metal sulfide deposited.

Effect of the initial TAA concentration

It is well known that the rate of H2S gas generation is a function of temperature, pH, and initial concentra-tion of TAA.38 At a given temperature and pH, the for-mation rate of H2S mainly depends on the initial con-centration of TAA. The precipitation of CuS in the pre-sent method is controlled by the slow diffusion of H2S gas originated from the decomposition of TAA in acidic solution. Therefore, the deposition rate of CuS is mostly controlled by the formation rate of H2S gas, which is determined by the initial concentration of TAA.

In order to investigate the dependence of the surface morphologies of the final hybrid microgels on the depo-sition rate of CuS, CuS-P(NIPAM-co-MAA) micro-spheres were prepared by using various initial concen-tration of TAA, specifically 0.43, 0.53, 0.60, and 0.80 mol/L, respectively, keeping the initial concentration of the Cu(Ac)2 solution at 0.3 mol/L. Figure 5 shows typi-cal SEM images of CuS-P(NIPAM-co-MAA) hybrid microgels produced by varying the TAA concentration. It can readily be observed that the surface textures of the hybrid microgels became clear and compact with in-creasing initial TAA concentration. For example, the hybrid microgels exhibit indistinct surface structures at lower initial TAA concentrations (Figure 5a). However, the wrinkled patterns of the hybrid microgels became more compact and denser with increasing TAA concen-tration (Figures 5b, 5c, and 5d).

It would seem reasonable to assume that the clear surface structures of the hybrid microgels were formed as a result of the rapid formation of CuS at the higher initial concentration of TAA. Actually, the diffusion rate of H2S gas was very slow as a result of controlling the decomposition of TAA in the acidic aqueous solu-tion. It can be envisaged that the local concentration of Cu2＋ ions continually decreased during the formation of CuS, and that free Cu2＋ ions in the inner part of the microgels then diffused to the reaction interface to make up this deficiency. The CuS deposition in this way may lead to an uneven density distribution of CuS between the interior and exterior of the polymer template. The surface networks deposited greater amount of CuS be-came more rigid, these networks were hard to contract, consequently, the wrinkled surface morphology of CuS-P(NIPAM-co-MAA) hybrid microgels could form after washing by acetone or drying. The deposition rate and amount of CuS would affect the distribution of CuS in the network of the hybrid microgels. Therefore, the initial influx rate of H2S gas may play a crucial role in the formation of the patterned surface structures of CuS-P(NIPAM-co-MAA) hybrid microgels.

In order to further study the effect of the precipita-tion rate of CuS on the surface morphology of the hy-

Preparation of CuS-P(NIPAM-co-MAA) Hybrid Microgels

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Figure 5 SEM images of CuS-P(NIPAM-co-MAA) hybrid microgels prepared at different initial concentration of TAA (mol/L), and their corresponding enlarged surface structures. (a) 0.43, (b) 0.53, (c) 0.60, (d) 0.80.

brid microgels, we conducted the following comparative experiments. For offering a condition of faster forming CuS, CuS-P(NIPAM-co-MAA) composite microspheres were prepared by introducing saturated H2S gas into the reaction system only instead of using TAA. It was demonstrated that the prepared CuS-P(NIPAM-co- MAA) composite microgels exhibited compactly wrin-kled structure (see the Supporting Information). It would seem reasonable to assume that the fast formation of CuS should be favorable for the greater amount of CuS on the surface. As a result, the easier shrinkage of the inner framework leads to formation of the compactly wrinkled surface structure.

Effect of the initial Cu(Ac)2 concentration

To study the effect of the amount of metal sulfide deposited on the patterned surface of the hybrid mi-crogels, CuS-P(NIPAM-co-MAA) composites were fabricated using Cu(Ac)2 solutions with different initial concentrations for swelling the template microgels. The

initial concentrations of Cu(Ac)2 were 0.10, 0.20, and 0.30 mol/L, respectively, and TAA solution concentra-tion was fixed at 0.53 mol/L. Observing the SEM im-ages, it can be found that the surface morphologies of the CuS-P(NIPAM-co-MAA) hybrid microgels became clearer and denser with increasing initial concentration of Cu(Ac)2 (Figure 6). When the initial concentration of Cu(Ac)2 was 0.1 mol/L, the hybrid microgels showed a faint patterned structure as shown in Figure 6a. When the initial concentration of Cu(Ac)2 was 0.2 mol/L, the surface of the hybrid microgels showed a broader wrin-kle (Figure 6b). When the initial concentration of Cu(Ac)2 was increased to 0.3 mol/L, the surface of CuS-P(NIPAM-co-MAA) hybrid microgels exhibited the obvious wrinkled structure (Figure 6c).

It can readily be envisaged that a higher initial con-centration of the reactants would lead to a relatively faster deposition rate and greater amount of CuS. The surface area of framework with greater amount of CuS

Figure 6 SEM images of CuS-P(NIPAM-co-MAA) hybrid microgels and their enlarged surface structures at different initial Cu(Ac)2

concentration (mol/L). (a) 0.10; (b) 0.20; (c) 0.30.

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would become more rigid. Consequently, the great dif-ference in rigidity between the inner and outside of framework resulted in the obvious difference in the contractibility for the two areas of the framework. Fi-nally, the clear and denser wrinkled surface structure would be easily formed. Therefore, the surface struc-tures of the hybrid microgels are significantly affected by the initial Cu(Ac)2 concentration.

Formation mechanism of patterned surface struc-tures of CuS-P(NIPAM-co-MAA) hybrid microgels

Based on the results mentioned above, the patterned surface structure of the CuS-P(NIPAM-co-MAA) hy-brid microgels are related to the uneven shrinkages of the networks of hybrid microgels due to the uneven deposition of CuS on the networks. The formation mechanism of the patterned surface structures of the CuS-P(NIPAM-co-MAA) hybrid microgels can be con-firmed by making a comparison between the swollen and shrunk behaviours of CuS-P(NIPAM-co-MAA) hybrid microgels. The swollen CuS-P(NIPAM-co-MAA) hybrid microgels and P(NIPAM-co-MAA) microgels quickly frozen in liquid nitrogen and then frozen-drying were carried out. The corresponding SEM images were shown in Figure 7. Comparing the surface morphologies shown in Figure 7(a, b, c) and Figure 7(d, e, f), one can easily observe that the network cavities of the obtained hybrid microgels became coarser and smaller than those of the pure microgels. It may be supposed that the Cu2＋ ions located at the outer part of the network were the first to encounter the H2S gas for formation of CuS. Subsequently, Cu2＋ ions in the inner part of the net-work gradually diffused to the surface for further for-

mation of CuS precipitation. The resulting precipitation process would lead to inward growth of CuS from the surface of the microspheres, which results in the uneven rigidity of frameworks from outer to inner because of the uneven distributed CuS on the frameworks. Clearly, the uneven rigidity of frameworks from outer to inner made their shrunk ability different. As a result, the wrinkled surface structure would form because CuS-P(NIPAM-co-MAA) hybrid microgels shrunk in the process of washing with acetone or drying (as shown in Figure 7c). However, for the pure microgels, there was not difference in rigidity between outer and inner of the framwork, this feature made the uniform shrinkage of the framwork, and the smooth surface would form as P(NIPAM-co-MAA) microgels shrunk (as shown in Figure 7f). The processes mentioned above were summarized in Scheme 1. From this mechanism, the relationship between the morphology of CuS- P(NIPAM-co-MAA) hybrid microgels and the condi-tions for in situ formation of CuS on P(NIPAM-co- MAA) microgels is easily understood. The surface morphology of the CuS-polymer composite micro-spheres not only depends on the guidance and confine-ment originated from the network of microgels template, but also on the formation rate and the amount of CuS deposited.

Based on the proposed mechanism, the effects of the initial TAA concentration and the initial Cu(Ac)2

concentration on the surface morphology of the composite microspheres could be reasonably explained. It is worthy to note that this mechanism is suitable not only for a given template microgel but also for some

Figure 7 SEM images of the CuS-P(NIPAM-co-MAA) hybrid microgels and P(NIPAM-co-MAA) microgels. The water-swollen sam-ple after freeze-drying (a, b and d, e) and air-drying (c, f).

Preparation of CuS-P(NIPAM-co-MAA) Hybrid Microgels

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Scheme 1 Schematic illustration of the formation mechanism of CuS-P(NIPAM-co-MAA) hybrid microgels with patterned surface structures

template microgels with the different composition. Namely, the effects of components and cross-linking degree of microgels on the surface patterns can be de-ducted. For example, with a greater amount of MAA in P(NIPAM-co-MAA) microgels, the wrinkled surface of CuS-P(NIPAM-co-MAA) should be more obvious due to an easier shrinkage for the microgel template con-taining great amount of MAA with flexible segments. the greater amount of cross-linker used in preparation of the microgel template, the patterned surface of CuS-P(NIPAM-co-MAA) should be obscure due to a hard shrinkage for denser cross-linked microgel tem-plate. In fact, the similar phenomena have been ob-served.32,34 In our opinion, the proposed mechanism could be successfully applied to explain some similar phenomena, and the principle involved in the proposed mechanism is universal to some extent.

Conclusions

In summary, CuS-P(NIPAM-co-MAA) hybrid mi-crogels with fancy surface patterns have been success-fully synthesized by the in situ reaction of Cu2＋ within the porous network of a P(NIPAM-co-MAA) microgels and H2S released by decomposition of TAA in acidic solution. By this way, the density of CuS trapped within the microgel template network is easily controlled by simply varying the initial concentrations of TAA and Cu2＋. The resulting precipitation process would lead to the formation of CuS on the networks from outer to in-ner, which results in the uneven rigidity of the frame-works. The surface structure derives from the different contractility of the frameworks during the hybrid mi-crogels drying. All factors that affect the deposition of metal sulfide can influence the surface morphology of the hybrid microgels. We have gained a deeper under-standing of the formation mechanism of the surface structures of metal sulfide-polymer hybrid microgels obtained by employing the polymer microgel template technique. Additionally, it is expected that the present research is useful for the controllable preparation of other inorganic-polymer hybrid microgels with complex surface morphologies.

Supporting information

SEM images of the P(NIPAM-co-MAA) microgels and the size distribution of CuS-P(NIPAM-co-MAA) hybrid microgels. In addition, SEM images of CuS-P(NIPAM-co-MAA) hybrid microgels prepared by introducing saturated H2S gas into the reaction system.

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