Poly(vinylpyridine) core/poly(N-isopropylacrylamide) shell microgel particles: their characterization and the uptake and release of an anionic surfactant

Monte Carlo simulation of the ionization and uptake behavior of cationic oligomers into pH-responsive polyelectrolyte microgels of opposite charge - a model for oligopeptide uptake and release

External stimuli can tune the uptake and release of guest molecules in microgels. Especially their pH responsiveness makes microgels exciting candidates for drug delivery systems. When both microgel and guest molecules are pH-responsive, predicting the electrostatically driven uptake can be complex since the ionization depends on many parameters. In this work, we performed Metropolis Monte Carlo simulations while systematically varying the pK of the monomers, the concentrations of microgel and guest molecules to obtain a better understanding of the uptake of weak cationic oligomers as a model for oligopeptides into a weak anionic polyelectrolyte microgel. Further, we varied the chain length of the oligomers. The polyelectrolyte networks can take up oligomers when both the network and the oligomers are charged. The presence of both species in the system leads to a mutual enhancement of their ionization. The uptake induces a release of counterions and results in complex formation between the oligomers and the network, leading to the collapse of the networks. Longer oligomers enhance the ionization of the network and, therefore, the complexation. A higher microgel concentration increases the uptake only around the isoelectric point but prevents the uptake due to lower entropy gain at counterion release at higher pH. The results give an insight into the uptake of cationic oligomers into oppositely charged polyelectrolyte microgels and provide hints for the design of anionic microgels as carriers for guest molecules e.g. antimicrobial peptides.

Ionisation and swelling behaviour of weak polyampholyte core-shell networks - a Monte Carlo study

The network charge of polyampholyte microgels can be tuned by varying the pH of the surrounding solution, and a charge reversal from a positively charged microgel at low pH to a negatively charged microgel at high pH can be achieved. In a titration experiment, it is difficult to tell apart the ionisation of the acidic and basic monomers in the network and to determine the distribution of charges in the network, whereas using Metropolis Monte Carlo simulations, both the degree of ionisation and the distribution of ionised monomers can be determined separately for both species. Building on our earlier work on alternating polyampholyte microgels, we now investigated the pH-dependent ionisation and the swelling behaviour of polyampholyte core-shell microgels under good solvent conditions. For this purpose, we performed Metropolis Monte Carlo simulations for a bead-spring model using the constant-pH method. As in our previous study on alternating microgels, the width of the U-shaped curve of the microgels volume as a function of pH depends on the relative dissociation constants of acid and base, and the microgel volume can be approximated by a linear function of the total network charge. Due to the spatial separation of acid and base in core-shell systems, the ionisation is less enhanced compared to a microgel with an alternating distribution of the two species. Nevertheless, we still see an influence of the presence of one species on the ionisation behaviour of the other species under good solvent conditions. Furthermore, the isoelectric point is shifted towards higher pH, which is caused by a higher charge density in the core compared to that in the shell. Added salt changes the Donnan equilibrium, which determines the counterion distribution within and outside of the microgel. At the same time, it contributes to the electrostatic screening of the network charges, leading to a narrowing of the U-shaped volume transition curve.

Antiseptic Materials on the Base of Polymer Interpenetrating Networks Microgels and Benzalkonium Chloride

Polymer microgels, including those based on interpenetrating networks (IPNs), are currently vastly studied, and their practical applications are a matter of thriving research. In this work, we show the perspective for the use of polyelectrolyte IPN microgels either as scavengers or carriers of antiseptic substances. Here, we report that poly-N-isopropylacrylamide/polyacrylic acid IPN microgels can efficiently absorb the common bactericidal and virucidal compound benzalkonium chloride. The particles can form a stable aqueous colloidal suspension or be used as building blocks for soft free-standing films. Both materials showed antiseptic efficacy on the examples of Bacillus subtilis and S. aureus, which was approximately equal to the commercial antibiotic. Such polymer biocides can be used as liquid disinfectants, stable surface coatings, or parts of biomedical devices and can enhance the versatility of the possible practical applications of polymer microgels.

Multiresponsive Microgels: Toward an Independent Tuning of Swelling and Surface Properties

Dual-responsive poly-(N-isopropylacrylamide) (PNIPAM) microgels surface-functionalized with polyethylene glycol (PEG) or poly-2-dimethylaminoethyl methacrylate (PDMAEMA) were developed to enable the swelling behavior and surface properties of the microgels to be tuned independently. The thermo-triggered swelling and pH-triggered surface properties of the microgels were investigated in aqueous suspensions using dynamic light scattering and on substrates using the surface forces apparatus. Grafting polymer chains on the microgel surface did not impede the thermo-triggered swelling behavior of the microgels in suspensions and immobilized on substrates. An unprecedented decoupling of the swelling behavior and surface properties could be obtained. More particularly, the thermo-triggered swelling behavior of the PNIPAM underlying microstructure could be tuned below and above the phase transition temperature with no change in the surface potential and adhesion provided by the surface non-responsive PEG.

Microphase separation of stimuli-responsive interpenetrating network microgels investigated by scattering methods

Polymer stimuli-responsive microgels find their use in various applications. The knowledge of its internal structure is of importance for further improvement and expanding the scope. Interpenetrating network (IPN) microgels may possess a remarkable feature of strongly non-uniform inner architecture, even microphase separation, in conditions of a selective solvent. In this research, we, for the first time, use a combination of static light scattering (SLS) and small-angle X-ray scattering (SAXS) techniques to collect the structure factors of aqueous dispersions of poly(N-isopropylacrylamide)-polyacrylic acid IPN microgels on the broad scale ofqvalues. We study the influence of solvent quality on microgel conformations and show that in a selective solvent, such a system undergoes microphase separation: the sub-network in a poor solvent conditions forms dense small aggregates inside the large swollen sub-network in a good solvent. We propose the microstructured sphere model for the IPN microgel structure factor interpretation and perform additional analysis and verification through coarse-grained molecular dynamics computer simulations.

Smart microgels as drug delivery vehicles for the natural drug aescin: uptake, release and interactions

In the present study, we show how acrylamide-based microgels can be employed for the uptake and release of the drug β-aescin, a widely used natural product with a variety of pharmacological effects. We show how aescin is incorporated into the microgel particles. It has an important influence on the structure of the microgels, by reducing their natural network-density gradient in the swollen state. Moreover, temperature-dependent measurements reveal how the incorporation of aescin stabilizes the microgel particles, while the volume phase transition temperature (VPTT) is almost constant, which is very important for the intended drug release. Finally, it is shown that upon increase of the temperature above the VPTT the particles are able to release aescin from their network, encouraging the use of this particular drug delivery system for hypothermia treatments.

Effect of Divalent Cation on Swelling Behavior of Anionic Microgels: Quantification and Dynamics of Ion Uptake and Release

Poly(N-vinylcaprolactam-co-itaconate) (P(VCL-co-IADME) microgels were synthesized varying the molar ratio between VCL and IADME via free radical precipitation polymerization in the presence of quaternary ammonium surfactant. In order to determine the effect of the divalent metal ions on the structure and the swelling behavior of the microgel systems, both neutral and charged forms of the hydrogels after hydrolysis were investigated. The triggered gel collapse caused by the divalent metal ion together with the quantification of the metal ion uptake was studied in detail by titration and ion chromatography methods and revealed the minimum concentration around 0.1 mM to trigger gel collapse on the treated gels. Uptake and release dynamics of the gels were followed by turbidity measurements and were in the time-range of 2 and 17 s, depending on the composition and the concentrations.

Microgels as efficient adsorbents for the removal of pollutants from aqueous medium

Due to their responsive behavior, high stability, and reusability, microgels have gained importance as adsorbents for the removal of aqueous pollutants such as heavy metals, nitroarenes, organic matter, and toxic dyes. However, there are few challenges that need to be addressed to make microgels as potential adsorbents for the removal of aqueous pollutants. This review article encircles the recent developments in the field of microgel usage as adsorbents for the extraction of aqueous pollutants. Many factors that influence the adsorption of pollutants such as pH, temperature of the medium, agitation time, pollutant concentration, microgel dose, and feed contents of microgels have been discussed in detail. Different adsorption isotherms as well as the kinetic and thermodynamic aspects of the adsorption process have also been enlightened to interpret the insight of the adsorption process. Microgel recovery from the reaction mixture as well as reusability is discussed from the financial point of view. The biodegradability of microgels induced due to the incorporation of specific biomacromolecules is also discussed.

Role of Anionic Surfactants in the Synthesis of Smart Microgels Based on Different Acrylamides

We investigated the influence of two anionic surfactants, namely, sodium dodecyl sulfate and sodium decyl sulfate, on acrylamide-based microgels consisting of N-n-propylacrylamide. In this context, the main focus was on the influence of surfactant addition on the size of the microgels. The surfactant was added to the reaction mixture before or during the polymerization at different points in time. Microgels were characterized via photon correlation spectroscopy and atomic force microscopy. All results were compared to those for other more common acrylamide-based microgels consisting of N-isopropylacrylamide and N-isopropylmethacrylamide. A significant difference between the three microgels and a strong dependence on the surface activity of the surfactant was found.

Rheology and structure of surface crosslinked surfactant-activated microgels

Nonionic surfactant-activated microgels (SAMs), composed of hydrophobic alkyl acrylates and hydrophilic hydroxyalkyl esters that utilize the effects of surfactant mediated swelling and interaction to provide pH-independent rheological properties, were previously reported as a new pathway to the rheology modification of surfactant solutions. Crosslinking was shown to play an important role in the properties of these soft microgel systems. To understand the impact of crosslinking chemistry on SAM polymers, we have compared two types of SAM polymers: a conventionally crosslinked SAM polymer via allyl pentaerythritol and a novel SAM polymer, where the surface is self-crosslinked via a reactive surfactant. We have systematically characterized the polymer's swelling, rheology and microstructure in a model system containing the polymer, sodium dodecyl sulfate (SDS) and water. Surface self-crosslinking is demonstrated to be a more effective crosslinking approach to create surfactant-mediated interactions between the microgel particles, resulting in more effective rheology modification. Internal crosslinking hinders both the full swelling of the SAM polymer as well as inter-particle bridging interactions, and is therefore less effective. To our best knowledge, this is the first report on creating a novel surface self-crosslinked microgel via a dual-functional reactive surfactant that interacts with a non-reactive surfactant to create a yield stress fluid.

Synthesis of pH- and ionic strength-responsive microgels and their interactions with lysozyme

Microgels composed of carboxymethyl cellulose (CMC) polymers via chemical crosslinking with sodium trimetaphosphate were synthesized and characterized using thermogravimetric analysis (TGA), swelling, and rheological analysis. The effects of pH, ionic strength, and crosslinking density on lysozyme loading in microgels were also studied. The microgel particle size ranged primarily from 10 to 20 μm. TGA revealed that the crosslinking increased the thermal stability of CMC. The swelling degree increased as pH increased from 3 to 5, and remained almost constant from pH 5 to 8. However, the swelling degree decreased with increasing ionic strength. The rheological analysis was in good agreement with the results of swelling degree. The protein uptake decreased with increasing ionic strength and crosslinking density. The pH 6 was the optimal pH for lysozyme absorption at ionic strength 0.05 M. The lysozyme-microgel complex was identified by confocal laser scanning microscopy, and the lysozyme distribution in the microgel was observed to be rather homogeneous.

Blending of reactive prepolymers to control the morphology and polarity of polyglycidol based microgels

The compartmentalization of microgels is a challenging task for synthetic polymer chemistry. Although the complexation with low molecular weight compounds or the use of microfluidic techniques offer attractive possibilities for other length scales, it is difficult to implement compartments in the mesoscale range of 10-100 nm. Herein we show how simple blending of reactive prepolymers is suitable to design new microgel morphologies with tailored compartments. We use poly(EEGE)-block-poly(AGE) as crosslinkable, pro-hydrophilic prepolymer in blends with varying amounts of crosslinkable, yet hydrophobic poly(THF-stat-AllylEHO) or inert and hydrophobic polystyrene, and crosslink the allyl functional prepolymer(s) in a thiol-ene click-type reaction after miniemulsification. Our strategy shows how arrested versus free nanophase separation can be used to control easily the morphology and polarity of microgel particles.

Construction of polyelectrolyte-responsive microgels, and polyelectrolyte concentration and chain length-dependent adsorption kinetics

We report on the construction of a polyelectrolyte-responsive system evolved from sterically stabilized protonated poly(2-vinylpyridine) (P2VPH(+)) microgels. Negatively charged sodium dodecylbenzenesulfonate (SDBS) surfactants could be readily internalized into the cationic microgels by means of electrostatic interactions, resulting in microgel collapse and concomitant formation of surfactant micellar domains (P2VPH(+)/SDBS)-contained electrostatic complexes. These internal hydrophobic domains conferred the opportunity of fluorescent dyes to be loaded. The obtained fluorescent microgel complexes could be further disintegrated in the presence of anionic polyelectrolyte, poly(sodium 4-styrenesulfonate) (PNaStS). The stronger electrostatic attraction between multivalent P2VPH(+) microgels and PNaStS polyelectrolyte than single-charged surfactant led to triggered release of the encapsulated pyrene dyes from the hydrophobic interiors into microgel dispersion. The process was confirmed by laser light scattering (LLS) and fluorescence measurements. Furthermore, the entire dynamic process of PNaStS adsorption into P2VPH(+) microgel interior was further studied by stopped-flow equipment as a function of polyelectrolyte concentration and degree of polymerization. The whole adsorption process could be well fitted with a double-exponential function, suggesting a fast (τ1) and a slow (τ2) relaxation time, respectively. The fast process (τ1) was correlated well with the approaching of PNaStS with P2VPH(+) microgel to form a nonequilibrium complex within the microgel shell, while the slow process (τ2) was consistent with the formation of equilibrium complexes in the microgel deeper inside. This simple yet feasible design augurs well for the promising applications in controlled release fields.

Relationship between temperature-induced changes in internal microscopic structures of poly(N-isopropylacrylamide) microgels and organic dye uptake behavior

Temperature-induced changes in the internal structures of poly(N-isopropylacrylamide) (pNIPAm) microgels were evaluated by small-angle X-ray scattering (SAXS), and the results were used to explain organic dye uptake by the microgels. The dye uptake experiments were conducted using two organic dyes: cationic rhodamine 6G (R6G) and anionic erythrosine. In the SAXS investigation, the internal structures of the microgels were characterized in terms of the correlation length, ξ, and the distance, d*, which originated from the local packing of the isopropyl groups of two neighboring chains. With increasing temperature up to the volume phase transition temperature (VPTT) of the microgels, the correlation length, ξ, was increased and the distance, d*, was decreased. At the same time, the amounts of the dyes taken up by the pNIPAm microgels were increased, despite a decrease in the volume of the microgels. The results indicated that the pNIPAm chains were closer to each other due to the hydrophobic association of isopropyl groups, which resulted in the growth of the hydrophobic domains. Thus, the hydrophobic interactions between the dyes and pNIPAm were probably accompanied by the domain formation. With a further increase of temperature above the VPTT, the correlation length, ξ, was decreased and then not defined because the Ornstein-Zernike type contribution disappeared, and the distance, d*, was not largely changed. At the same time, the uptake amounts of the dyes per unit volume of the microgels were also not largely changed, which behaved similar to the distance, d*. It was probably due to the fact that the internal structures of the microgels were not largely changed because the isopropyl groups were in contact with each other. The view was supported by the result of the uptake study of the nonthermoresponsive microgels which did not have the hydrophobic isopropyl groups.

Thermosensitive ionic microgels via surfactant-free emulsion copolymerization and in situ quaternization cross-linking

A type of thermosensitive ionic microgel was successfully prepared via the simultaneous quaternized cross-linking reaction during the surfactant-free emulsion copolymerization of N-isopropylacrylamide (NIPAm) as the main monomer and 1-vinylimidazole or 4-vinylpyridine as the comonomer. 1,4-Dibromobutane and 1,6-dibromohexane were used as the halogenated compounds to quaternize the tertiary amine in the comonomer, leading to the formation of a cross-linking network and thermosensitive ionic microgels. The sizes, morphologies, and properties of the obtained ionic microgels were systematically investigated by using transmission electron microscopy (TEM), dynamic and static light scattering (DLS and SLS), electrophoretic light scattering (ELS), thermogravimetric analyses (TGA), and UV-visible spectroscopy. The obtained ionic microgels were spherical in shape with narrow size distribution. These ionic microgels exhibited thermosensitive behavior and a unique feature of poly(ionic liquid) in aqueous solutions, of which the counteranions of the microgels could be changed by anion exchange reaction with BF4K or lithium trifluoromethyl sulfonate (PFM-Li). After the anion exchange reaction, the ionic microgels were stable in aqueous solution and could be well dispersed in the solvents with different polarities, depending on the type of counteranion. The sizes and thermosensitive behavior of the ionic microgels could be well tuned by controlling the quaternization extent, the type of comonomer, halogenated compounds, and counteranions. The ionic microgels showed superior swelling properties in aqueous solution. Furthermore, these ionic microgels also showed capabilities to encapsulate and release the anionic dyes, like methyl orange, in aqueous solutions.

A study on dispersion and characterisation of α-mangostin loaded pH sensitive microgel systems

BACKGROUND

α-Mangostin was extracted with methanol from the rind of mangosteen fruit and purified by using silica gel column chromatography technique. The compound is characterised using infrared, (13)C and (1)H NMR as well as UV-vis spectroscopy. The α-mangostin dispersion in colloidal systems was studied by incorporating it with an ionic microgel, poly (N-Isopropylacrylamide)-co-2VP at different pH.

RESULT

The DLS result showed the size of microgel-α-mangostin mixture declined from 548 nm to 200 nm upon the increment of the pH. Moreover, it was found the morphology of loaded compound depended largely on the nature of the continuous phase of the microgel system. Interestingly, by manipulating the pH, α-mangostin tends to form crystal at extremely low pH and transforms into spherical shapes at pH 6.

CONCLUSION

This research shows different structures of the α-mangostin particle that are attributed by adjusting the pH using microgel systems as a template.

Effect of chain length on the interaction between modified organic salts containing hydrocarbon chains and poly(N-isopropylacrylamide-co-acrylic acid) microgel particles

A series of four hydrophobically modified, diphenylazo-based organic salts have been prepared and characterized. To achieve this a C(x) (x = 4, 6, 8, or 10) hydrocarbon chain was inserted between the diphenylazo moiety and the quaternary ammonium headgroup of the salt. The absorption of each of the four modified organic salts into anionic microgel particles of poly(N-isopropylacrylamide-co-acrylic acid) has been studied at pH 8. In addition, the hydrodynamic diameters and electrophoretic mobilities of the microgel particles have been studied as a function of the organic salt concentration, also at pH 8. In addition to the electrostatic attraction between the quaternary ammonium head groups of the organic salts and the anionic groups within the microgel particles, hydrophobic association between the chains of the organic salts within the microgel particles plays a role, with this effect increasing strongly from x=4 to 10. Desorption of the x=4 and 6 organic salts occurs readily on changing, in situ, the pH from 8 to 2.5 (and thereby eliminating the electrostatic interaction) but is only partially achieved for the x=8 and 10 organic salts. Indeed, for the x=10 organic salt, only about 80% of the organic salt is desorbed upon dilution of the microgel particles into a large excess of water.

Controlling gold nanoparticle stability with triggerable microgels

The interaction of a photodegradable surfactant (PS, 4-hexylphenylazosulfonate, C(6)PAS) with microgels (MGs) of poly(2-vinyl pyridine) (MGA) in the protonated state (pH 3) has been investigated. Electrophoretic mobility measurements confirm that negatively charged PS interacts with positively charged MGA to form mixed PS-MG complexes. This was sensed by a decrease in the effective PS-MGA charge and a switch in sign of electrophoretic mobility, from positive to negative, with increasing PS concentration. After the addition of extra positive microgels (MGB), the system undergoes coflocculation. Incident UV irradiation was used to photolyze the anionic PS, effectively eliminating the headgroups, thereby lowering the electrostatic interactions between PS and MGA microgel networks. Consequently, a reversal of MGA charge occurred, leading to electrostatic repulsions and causing the MGs to reswell and redisperse, with both MGA and MGB now being positively charged and hence stabilized against coflocculation. Extending this approach, negatively charged gold nanoparticles (AuMES) have been incorporated into the PS-MGA complexes. Atomic absorption spectroscopy (AAS) showed that 100% of the AuMES particles were recovered after coflocculation of (PS-MGA)-AuMES complexes with MGB. Furthermore, approximately 75% of the AuMES could be redispersed after UV irradiation to restabilize the dispersion. This system provides an interesting method for phase separation and gold nanoparticle recovery for reuse and recycling.

Amphoteric core-shell microgels: contraphilic two-compartment colloidal particles

pH-responsive amphoteric core-shell microgel particles were synthesized by emulsion copolymerization of the appropriate functional monomers with ethylene glycol dimethacrylate as the cross-linker. 2-(Diethylamino)ethyl methacrylate (DEA) was used as the ionizable basic monomer, and tert-butyl methacrylate served as the hydrophobic monomer precursor, which gave the methacrylic acid (MAA) moieties following acid hydrolysis of the ester groups. The core of the polyampholyte microgels comprised a cross-linked poly(2-(diethylamino)ethyl methacrylate) (PDEA) or poly(methacrylic acid) (PMAA) network surrounded by a cross-linked PMAA or PDEA shell, respectively. A polyampholyte random copolymer microgel with the DEA and MAA units randomly distributed within the gel phase was also prepared. Scanning electron microscopy studies showed spherical particles of a narrow size distribution, and transmission electron microscopy verified the core-shell topology of the particles. Potentiometric titration curves revealed two plateau regions for the polyampholyte core-shell microgels attributed to the independent ionization process of the core and the shell of the particles, in contrast to the random copolymer microgel particles that exhibited a single plateau region as a result of the simultaneous protonation/deprotonation process of the basic and acidic moieties of the microgels. The core and the shell of the particles were found to swell independently upon ionization of the DEA or MAA moieties at low or high pH, respectively, whereas collapsed latex particles were obtained in the intermediate pH range when both the core and the shell of the particles were neutral, in agreement with the potentiometric titration data. These core-shell microgels comprise novel two-compartment nanostructures that exhibit contraphilic properties in the core and the shell of the particles in response to a single external stimulus.

The uptake and release of cationic surfactant from polyampholyte microgel particles in dispersion and as an adsorbed monolayer

The use of novel polyampholyte microgel particles for the controlled absorption and release of a cationic surfactant has been investigated. The addition of cetylpyridinium chloride (CPC) to aqueous dispersions of poly(2-diethylamino)ethyl methacrylate-co-methacrylic acid (DEAEM-co-MAAc) microgel particles has been studied with respect to CPC concentration and solution pH. CPC was found to absorb into the polyampholyte microgel particles, resulting in reduced hydrodynamic diameter and electrophoretic mobility, when added to microgel dispersion at pH 11. Strong desorption could be induced by switching the pH from 11 to 3, with most of the desorption occurring in the region of the isoelectric pH of the particles. The properties of surface-adsorbed monolayers of polyampholyte microgel particles were also investigated, both in the presence and absence of CPC. The substrate surface charge was found to influence the swelling profile of the adsorbed microgel monolayers. The interaction of CPC surfactant with monolayers of adsorbed microgel particles shows strong correlations with the interaction of CPC surfactant with microgel particles in dispersion.

Oligo(ethylene glycol)-based thermoresponsive core-shell microgels

Oligo(ethylene glycol)-based thermoresponsive core-shell microgels were synthesized by a two-step polymerization method: The core particles mainly consisted of poly(ethylene glycol) ethyl ether methacrylate (PEGEEMA), while the shell mainly consisted of a copolymer of PEGEEMA, poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), and poly(acrylic acid). The copolymerization of the shell resulted in a higher volume phase transition temperature than that of the core. The mass of a single microgel particle was determined by both the static light scattering method and a new method using UV-visible spectroscopy. Core-shell microgels in water self-assembled into crystalline structures with iridescent colors, which were the result of Bragg diffraction. The melting kinetics of microgel crystals was studied by using UV-visible transmission spectroscopy.

Preparation and properties of thermo-sensitive organic/inorganic hybrid microgels

By utilizing the hydrolysis and condensation of the methoxysilyl groups, thermo-sensitive organic/inorganic hybrid poly[ N-isopropylacrylamide- co-3-(trimethoxysilyl)propylmethacrylate] [P(NIPAm- co-TMSPMA)] microgels were successfully prepared via two different methods without addition of any surfactant. First, the microgels were obtained by a two-step method; that is, the linear copolymer P(NIPAm- co-TMSPMA) was first synthesized by free radical copolymerization, and the aqueous solution of the copolymer was then heated above its low critical solution temperature (LCST) to give colloid particles, which were subsequently cross-linked via the hydrolysis and condensation of the methoxysilyl groups to form the microgels. Second, the microgels were also prepared via conventional surfactant-free emulsion polymerization (SFEP) of the monomers NIPAm and TMSPMA. TMSPMA can act as the cross-linkable monomer. No surfactant was involved in the preparation of the hybrid microgels. The obtained microgels were rather spherical and exhibited reversible thermo-sensitive behavior. The size, morphology, swellability, and phase transition behavior of the microgels were dependent on the initial copolymer or monomer concentration, preparation temperature, and the content of TMSPMA. The size of microgels obtained by SFEP was found to be more uniform than that by the two-step method. The hybrid microgels obtained by these two methods had more homogeneous microstructures than those prepared via conventional emulsion polymerization with chemical cross-linker N, N'-methylene-bisacrylamide.