“Smart” membrane materials: Preparation and characterization of PVDF‐g‐PNIPAAm graft copolymer

In this research, a smart membrane material of graft copolymer of poly(vinylidene fluoride) with poly(N‐isopropylacrylamide) (PVDF‐g‐PNIPAAm) was synthesized by atom transfer radical polymerization (ATRP) using poly(vinylidene fluoride) (PVDF) as a macroinitiator and direct initiation of the secondary fluorinated site PVDF facilitates grafting the N‐isopropylacrylamide comonomer. The copolymers were characterized by Fourier transform infrared (FTIR), ¹H NMR, gel‐permeation chromatography (GPC), and X‐ray photoelectron spectroscopy (XPS). The temperature‐sensitive membrane was prepared from the PVDF‐g‐PNIPAAm graft copolymers by the phase inversion method. The effects of temperature on the flux of pure water of membrane was investigated. The results showed that alkyl fluorides were successfully applied as ATRP initiators in the synthetic condition and the flux of pure water through the PVDF‐g‐PNIPAAm membrane depended on the temperature change. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1482–1486, 2007     

Poly(ε‐caprolactone)‐graft‐poly(N‐isopropylacrylamide) amphiphilic copolymers prepared by a combination of ring‐opening polymerization and atom transfer radical polymerization: Synthesis,self‐assembly,and thermoresponsive property

Thermoresponsive graft copolymers of ε‐caprolactone and N‐isopropylacrylamide were synthesized by a combination of ring‐opening polymerization and the sequential atom transfer radical polymerization (ATRP). The copolymer composition, chemical structure, and the self‐assembled structure were characterized. The graft length and density of the copolymers were well controlled by varying the feed ratio of monomer to initiator and the fraction of chlorides along PCL backbone, which is acting as the macroinitiator for ATRP. In aqueous solution, PCL‐g‐PNIPAAm can assemble into the spherical micelles which comprise of the biodegradable hydrophobic PCL core and thermoresponsive hydrophilic PNIPAAm corona. The critical micelle concentrations of PCL‐g‐PNIPAAm were determined under the range of 6.4–23.4 mg/L, which increases with the PNIPAAm content increasing. The mean hydrodynamic diameters of PCL‐g‐PNIPAAm micelles depend strongly on the graft length and density of the PNIPAAm segment, allowing to tune the particle size within a wide range. Additionally, the PCL‐g‐PNIPAAm micelles exhibit thermosensitive properties and aggregate when the temperature is above the lower critical solution temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41115.     

Synthesis and characterization of polyrotaxanes comprising α-cyclodextrins and poly(ε-caprolactone) end-capped with poly(N-isopropylacrylamide)s

Biodegradable polyrotaxane (PR)-based triblock copolymers were synthesized via the atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAm) initiated with polypseudorotaxanes (PPRs) consisting of a distal 2-bromopropiomyl bromide end-capping poly(ε-caprolactone) (Br-PCL-Br) and a varying amount of α-cyclodextrins (α-CDs) in the presence of Cu(I)Br/PMDETA at 25 °C in aqueous solution. The copolymers were featured by relatively higher yields from 46.0% to 82.8% as compared with previous reports. Their structure was characterized in detail by using ¹H NMR, ¹³C CP/MAS NMR, GPC, WXRD, DSC and TGA analyses. When a feed molar ratio of NIPAAm to Br-PCL-Br was changed from 50 to 200, the degree of polymerization of PNIPAAm blocks attached to two ends of PPRs was in a range of 158–500. About one third of the added α-CDs were still entrapped on the central PCL chain after the ATRP process. Attaching PNIPAAm rendered the copolymers soluble in aqueous solution showing the thermo-responsibility as evidenced by turbidity measurements.     

Synthesis of star poly(N-isopropylacrylamide) by β-cyclodextrin core initiator via ATRP approach in water

Star poly(N-isopropylacrylamide) (PNIPAAm) based on a β-cyclodextrin (β-CD) core macroinitiator was synthesized by means of atomic transfer radical polymerization (ATRP) in water using copper(I)/2,2bipyridyl complex as a catalytic system at temperature above the lower critical solution temperature (LCST) of the PNIPAAm. The macroinitiator was prepared by the transesterification reaction of the (β-CD) with 2-bromopropionyl bromide. The LCST of the samples upshifts slightly when the absolute molecular mass of the star PNIPAAm increases. Over the phase transition, the solutions became bluish opalescent due to formation of a heterogeneous phase system consisting of collapsed polymer particles in water. Atomic force microscopy and dynamic light scattering analyses indicated two populations of self-assembled polymer structure: a larger population and a smaller population. The smaller size suggests to self-assembly of polymer micelles and the large one corresponds to aggregates of polymer micelles or star polymers coupled. Polydispersity of the star PNIPAAm ranged from 1.60 to 4.04 within 15 h of reaction, which was attributed to the collapse of the PNIPAAm chains at temperature above the LCST that causes a decrease of the polymer reactivity. This was also attributed to the star–star coupling that generates twice the value of the polydispersity for any time before 15 h of polymerization.     

Synthesis and characterization of dual responsive graft copolymers composed of casein and poly(N-isopropylacrylamide)

A series of novel temperature- and pH- responsive water-soluble graft copolymers, casein-g-poly(N-isopropylacrylamide)(PNIPAAm), were prepared via a direct graft copolymerization of N-Isopropylacrylamide (NIPAAm) from casein. The polymerization was induced by tert-butyl hydroperoxide (TBHP) in water at general condition. Chemical structures of the graft copolymers were characterized by Fourier transform infrared spectra (FTIR), Thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effect elements on graft copolymerization, such as concentration of initiator, reaction time, reaction temperature and ratio of NIPAAm to casein were investigated in terms of NIPAAm conversion, grafting percentage (GP) and grafting efficiency (GE), respectively. The graft copolymers are stimuli-sensitive with respect to both temperature and pH in aqueous solutions. It could self-assembly into core-shell particles in aqueous solution with collapsed PNIPAAm as core as well as inverse core-hair particles with expanded casein as core on changing temperature or pH, as indicated by transmission electron microscopy (TEM).     

Synthesis and electrorheological characteristics of titanate nanotube suspensions under oscillatory shear

In this study, titanate nanotubes (TNTs) were synthesized by hydrothermal treatment of TiO₂ powders (P25) in a NaOH solution. The as-synthesized TNTs exhibit high surface area and large aspect ratio. Rheological properties of TNTs suspensions were then investigated under oscillatory shear. The TNTs fluid shows the viscoelastic behavior and the dynamic moduli (G′, G″) increase significantly by about 4 orders of magnitude as the electric field strength is up to 2.0 kV/mm. Transient response under dynamic shear reveals different changes in the microstructure of TNTs fluid from steady shear. The complex modulus of TNTs fluids is sensitive to temperature while that of P25 fluid become insensitive at higher temperature. Dynamic viscoelastic behavior suggests that structure of P25 to TNTs transition merits the enhancement of ER activity of TNTs fluid.     

Hydrothermal synthesis of mesoporous TiO<Subscript>2</Subscript> nanotubes and their adsorption affinity toward Basic Violet 2

Hydrothermal method was used to synthesize TiO₂ nanotubes (TNTs), which are considered as a novel adsorbent with high surface area and adsorption capacity. Different methods including X-ray diffraction (XRD), transmission electron microscope (TEM) and Brunauer–Emmett–Teller (BET) analysis were used to investigate and identify synthesized TNTs. The adsorption capacity of TNTs was investigated with regard to removing Basic Violet 2 (BV2) as a model organic pollutant from aqueous solution. The mean outer, inner diameter and thickness of the TNTs were found to be approximately 9, 4 and 2.5 nm, respectively. BET–BJH method was used for measuring specific surface area and pore volume of the TNTs which turned out to be 200.38 m² g^?1 and 0.44 cm³ g^?1, respectively. The results of the study indicated synthesized TNTs may be considered as efficient and effective adsorbent for removing BV2 (75.63%) from aqueous solution. The impact of the operational variables, i.e. initial BV2 concentration (2–20 mg L^?1), dosage of adsorbent (0.01–0.6 g), and pH (2–8) in relation to the adsorption capacity of BV2 onto TNTs were investigated. The experimental results of the study were meticulously taken into consideration for discussing and analyzing the adsorption isotherms and kinetics. It was found that the collected experimental data regarding the kinetic and isotherm examinations were compatible and well-matched with the pseudo-first order kinetic model and Langmuir isotherm model (R ²?=?0.9634).     

Synthesis of block copolymers for surface functionalization with stimuli-responsive macromolecules

Using block copolymers with poly(n-butyl acrylate) (PBA) as anchor block being capable to tether the temperature-responsive block poly(N-isopropylacrylamide) (PNIPAAm) to the surface, polysulfone (PSf) films were functionalized applying an adsorption/surface entrapment process. Homo and block copolymer synthesis was investigated applying atom transfer radical polymerization (ATRP) using tris(2-(dimethylamino)ethyl)amine (Me₆TREN), CuCl and N,N-dimethylformamide (DMF). On basis of the determined critical micelle concentration of the block copolymers, surface functionalization of PSf was performed from an aqueous solution containing 25 vol% dimethylacetamide. These functionalized surfaces exhibit reversible temperature dependent properties due to the lower critical solution temperature (LCST) of PNIPAAm as can be proven by contact angle measurement. Furthermore, the beneficial effect of the PBA block with adjusted molecular weight on the stability of these coatings was proven. This surface functionalization method has various potential applications and the resulting surfaces are anticipated to exhibit actively triggerable ‘chaotic’ properties as basis of an efficient anti-biofouling strategy.     

Fabrication of hybrid nanocomposites with polystyrene and multiwalled carbon nanotubes with well-defined polystyrene via multiple atom transfer radical polymerization

The PS-grafted multiwalled carbon nanotubes (MWNTs) were produced by the bromo-ended PS (PS-Br) and pristine MWNTs in 1,2-dichlorobenzene at 110 °C for 72 h via atom transfer radical polymerization (ATRP). Bromo-ended PS (PS-Br) used as an initiator for the functionalization of MWNTs was synthesized with styrene by ATRP conditions using CuBr and N,N,N′,N′,N″-pentamethyldiethylenetriamine as catalyst. The PS-grafted MWNTs were fully characterized by ¹H-NMR, FT-IR, DSC, TGA, and SEM. The PS-grafted MWNTs were found to be highly soluble in a variety of organic solvents. The PS was chemically attached to the surfaces of MWNTs via ATRP approach, and the grafting amount of PS was 40–90%. From TGA and DSC measurements, the PS-grafted MWNTs were decomposed at lower temperature compared to that of PS-Br, and the functionalization of MWNTs increased the glass-transition temperature (T_g) of the grafted PS. The PS/PS-grafted MWNTs nanocomposites were prepared with PS and PS-grafted MWNTs by solution mixing in dimethylformamide (DMF). The resulting nanocomposites were found to be the homogeneous dispersion of PS-grafted MWNTs in PS matrix via aromatic (π–π) interactions between PS and PS-grafted MWNTs as determined by SEM and TEM.     

Synthesis and characterization of well-defined hydrophilic block copolymer brushes by aqueous ATRP

Homopolymer brushes of poly(N,N-dimethylacrylamide) (PDMA), poly(methoxyethylacrylamide) (PMEA) and poly(N-isopropylacrylamide)(PNIPAM) grown on atom transfer radical polymerization (ATRP) initiator functionalized latex particles were used as macroinitiators for the synthesis of PDMA-b-PNIPAM/PMEA, PMEA-b-PDMA/PNIPAM and PNIPAM-b-PDMA block copolymer brushes by surface initiated aqueous ATRP. The grafted homopolymer and block copolymer brushes were analyzed for molecular weight, molecular weight distribution, chain grafting density, composition and hydrodynamic thickness (HT) using gel permeation chromatography-multi-angle laser light scattering, ¹H NMR, particle size analysis and atomic force microscopy (AFM) techniques. The measured graft molecular weight increased following the second ATRP reaction in all cases, indicating the second block had been added. Chain growth depended on the nature of the monomer used for block copolymerization and its concentration. Unimodal distribution of polymer chains in GPC with non-overlap of molar mass-elution volume curves implied an efficient block copolymerization. This was supported by the increase in HT measured by particle size analysis, equilibrium thickness observed by AFM and the composition of the block copolymer layer by ¹H NMR analysis, both in situ and on cleaved chains in solution. ¹H NMR analysis of the grafted latex and cleaved polymers from the surface demonstrated that accurate determination of the copolymer composition by this method is possible without detaching polymer chains from surface. Block copolymer brushes obey the same power law dependence of HT on molecular weight as homopolymer brushes in good solvent conditions. The NIPAM-containing block copolymer brushes were sensitive to changes in the environment as shown by a decrease in HT with increase in the temperature of the medium.     

Graft copolymerization of methylmethacrylate with N‐substituted maleimide‐styrene copolymer by ATRP

Atom transfer radical polymerization (ATRP) was employed to prepare graft copolymers having poly(MBr)‐alt‐poly(St) copolymer as backbone and poly(methyl methacrylate) (PMMA) as branches to obtain heat resistant graft copolymers. The macroinitiator was prepared by copolymerization of bromine functionalized maleimide (MBr) with styrene (St). The polymerization of MMA was initiated by poly(MBr)‐alt‐poly(St) carrying bromine groups as macroinitiator in the presence of copper bromide (CuBr) and bipyridine (bpy) at 110°C. Both macroinitiator and graft copolymers were characterized by ¹H NMR, GPC, DSC, and TGA. The ATRP graft copolymerization was supported by an increase in the molecular weight (MW) of the graft copolymers as compared to that of the macroinitiator and also by their monomodal MW distribution. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

In-situ study of the structure and dynamics of thermo-responsive PNIPAAm grafted on a cotton fabric

Stimuli-responsive polymeric materials can adapt to various surrounding environments, converting chemical and biochemical changes into optical, electrical and thermal signals, or changing wettability and adhesion properties upon external stimuli. Herein we report a cotton fabric modified with a thermo-responsive polymer, Poly(N-isopropylacrylamide) (PNIPAAm). ¹H solid-state NMR techniques were used to characterize the molecular structure and dynamics of the PNIPAAm brushes, while still grafted on the cotton fabric surfaces, avoiding un-grafting destructive procedures. The results demonstrate that the motion of the grafted PNIPAAm brushes is restricted as the temperature rises above the low critical solution temperature (LCST), which was estimated to be ～34 °C. Variable temperature (VT) experiments were used to investigate the nature of the hydrophilic-hydrophobic transitions of the grafted polymer. The ¹H solid-state NMR techniques used proved to be an extremely sensitive and precise way to probe in-situ the LCST transition of the PNIPAAm brushes, while still grafted on cotton fibres.This work presents a high potential synthesis and analysis route towards stimuli-responsive cotton fibres which can find exceptional applications as novel intelligent fabrics for the textile related industries.     

Synthesis of poly(styrene-co-acrylonitrile) copolymer brushes on silica nanoparticles through surface-initiated polymerization

In the present investigation, silica nanoparticles have been coated with poly(styrene-co-acrylonitrile) (SAN) copolymer brushes synthesized via surface-initiated atom transfer radical polymerization (ATRP). In the initial step, silica nanoparticles were functionalized with triethoxysilane-based ATR initiator, 6-(2-bromo-2-methyl) propionyloxy hexyl triethoxysilane. Successful formation of the covalent linkages between ATRP initiator and silica nanoparticles is further corroborated using thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The surface initiated ATRP of the styrene and the acrylonitrile mediated by a copper complex was carried out using the initiator fixed silica nanoparticles in the presence of a sacrificial (free) initiator. The polymerization is preceded in a living manner in all examined cases, producing nanoparticles coated with well-defined poly(styrene-co-acrylonitrile) (SAN) brushes with molecular weight in the range of 12–22 kDa. SAN-grafted silica nanoparticles were characterized using TGA which showed significant weight loss in the temperature range of 340–420 °C confirming the formation of the polymer brushes on the surface with graft densities in the range of 0.109–0.190 chains/nm². Successful formation of the SAN copolymer brushes are further characterized by FTIR and proton nuclear magnetic resonance spectroscopy techniques. Differential scanning calorimetric studies revealed that the SAN copolymer grafted onto silica nanoparticles exhibits higher glass transition temperatures than free SAN copolymers. Transmission electron microscopy and dynamic light scattering studies revealed that the SAN copolymer-grafted silica nanoparticles showed relatively fine dispersion in organic solvents such as tetrahydrofuran, when compared to bare silica nanoparticles.     

Graft copolymers prepared by atom transfer radical polymerization (ATRP) from cellulose

A cellulose-based macro-initiator, cellulose 2-bromoisobutyrylate, for atom transfer radical polymerization (ATRP) was successfully synthesized by direct homogeneous acylation of cellulose in a room temperature ionic liquid, 1-allyl-3-methylimidazolium chloride, without using any catalysts and protecting group chemistry. ATRP of methyl methacrylate and styrene from the macro-initiator was then carried out. The synthesized cellulose graft copolymers were characterized by FTIR, ¹H NMR and ¹³C NMR spectroscopies. The grafted PMMA and PS chains were obtained by the hydrolysis of the cellulose backbone and analyzed by GPC. The results obtained from these analytical techniques confirm that the graft polymerization occurred from the cellulose backbone and the obtained copolymers had grafted polymer chains with well-controlled molecular weight and polydispersity. Through static and dynamic laser light scattering and TEM measurements, it was found that the cellulose graft copolymer in solution could aggregate and self-assembly into sphere-like polymeric structure.     

Preparation of thermal‐responsive poly(propylene) membranes grafted with n‐isopropylacrylamide by plasma‐induced polymerization and their water permeation

Poly(propylene) (PP) membrane grafted with poly(N‐isopropylacrylamide) (PNIPAAm), which is known to have a lower critical solution temperature (LCST) at around 32°C, was prepared by the plasma‐induced graft polymerization technique. Graft polymerization of PNIPAAm onto a PP membrane was confirmed by microscopic attenuated total reflection/Fourier transform IR spectroscopy. The grafting yield of PNIPAAm increased with the concentration of N‐isopropylacrylamide monomer and the reaction time of graft polymerization. The average pore size of the PP membrane also affected the grafting yield. From the field emission scanning electron microscopy (FE‐SEM) measurement, we observed a morphological change in the PP‐g‐PNIPAAm membrane under wet conditions at 25°C below LCST. The permeability of water through the PP‐g‐PNIPAAm membrane was controlled by temperature. The PP‐g‐PNIPAAm membrane (PN05 and PN10) exhibited higher water permeability (L_p) than the original PP substrate membrane below LCST. As the temperature increased to above LCST, L_p gradually decreased. In addition, the graft yield of PNIPAAm and the average pore size of the PP substrate influenced water permeability. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1168–1177, 2002; DOI 10.1002/app.10410     

Synthesis and thermally responsive characteristics of dendritic poly(ether-amide) grafting with PNIPAAm and PEG

A series of thermally responsive dendritic core-shell polymers were prepared based upon dendritic poly(ether-amide) (DPEA), modified with carboxyl end-capped linear poly(N-isopropylacrylamide) (PNIPAAm-COOH) or both PNIPAAm-COOH and carboxyl end-capped methoxy polyethylene glycol (PEG-COOH) in different ratios via an esterification process to obtain DPEA-PNIPAAm or DPEA-PNIPAAm-PEG. Their molecular structures were verified by gel permeation chromatography, and ¹H NMR and FTIR spectroscopy. The temperature-dependent characteristics study has revealed that DPEA-PNIPAAm exhibits a lower critical solution temperature (LCST) of about 34 °C, whereas DPEA-PNIPAAm-PEG polymers with the PNIPAAm/PEG ratio of about 1.0 and 0.4 possess about 36 °C and 39 °C, respectively, compared with 32 °C for homopolymer PNIPAAm. The critical aggregation temperature was investigated using fluorescence excitation spectrum of pyrene as a sequestered guest molecule based upon the sharp increase of the I₃₃₈/I₃₃₃ value.     

Surface-initiated atom transfer radical polymerization of methyl methacrylate on magnetite nanoparticles

The synthesis of magnetite nanoparticles coated with a well-defined graft polymer is reported. The magnetite nanoparticles with an initiator group for copper-mediated atom transfer radical polymerization (ATRP), 2-(4-chlorosulfonylphenyl) ethyltrichlorosilane (CTCS) chemically bound on their surfaces were prepared by the self-assembled monolayer-deposition method. The surface-initiated ATRP of methyl methacrylate (MMA) was carried out with the CTCS-coated magnetite nanoparticles in the presence of free (sacrificing) initiator, p-toluenesulfonyl chloride. Polymerization proceeded in a living fashion, exhibiting first-order kinetics of monomer consumption and a proportional relationship between molecular weight of the graft polymer and monomer conversion, thus providing well-defined, low-polydispersity graft polymers with an approximate graft density of 0.7 chains/nm². The molecular weight and polydispersity of the graft polymer were nearly equal to those of the free polymer produced in the solution, meaning that the free polymer is a good measure of the characteristics of the graft polymer. The graft polymer possessed exceptionally high stability and remarkably improved dispersibility of the magnetite nanoparticles in organic solvent.     

Optically active thermosensitive amphiphilic polymer brushes based on helical polyacetylene: preparation through “click” onto grafting method and self-assembly

Optically active, thermosensitive, and amphiphilic polymer brushes, which consist of helical poly(N-propargylamide) main chains and thermosensitive poly(N-isopropylacrylamide) (PNIPAm) side chains, were prepared via a novel methodology combining catalytic polymerization, atom transfer radical polymerization (ATRP), and click chemistry. Helical poly(N-propargylamide) bearing α-bromoisobutyryl pendent groups was synthesized via catalytic polymerization, followed by substituting the –Br moieties with azido groups. Then, alkynyl terminated PNIPAm formed via ATRP was successfully grafted onto the azido functionalized helical polymer backbones via click chemistry, providing the expected polymer brushes. GPC, FT-IR, and ¹H-NMR measurements indicated the successful synthesis of the novel amphiphilic polymer brushes. UV–vis and CD spectra evidently demonstrated the helical structures of the polymer backbones and the considerable optical activity of the final brushes. The polymer brushes self-assembled in aqueous solution forming core/shell structured nanoparticles, which were comprised of optically active cores (helical polyacetylenes) and thermosensitive shells (PNIPAm).     

Adsorption of Cu2+ ions with poly(N‐isopropylacrylamide‐co‐methacrylic acid) micro/nanoparticles

Chelation efficiency of stimuli‐responsive poly(N‐iospropylacrylamide‐co‐methyacrylic acid) (PNIPAAm‐MAA) nanoparticles with Cu²⁺ ions from CuSO₄·5H₂O solution and from wood treated with copper‐based preservatives was studied. It was shown that particle size played a very important role in the adsorption process. The nano‐scale particles showed much improved Cu ion adsorption efficiency, compared with the micro hydrogels. The amount of Cu ion adsorption increased with increase of MAA ratio in copolymers and adsorption efficiency decreased with increased particle size. Furthermore, the adsorption amount varied with adsorption temperature at temperatures both below and above the corresponding low critical solution temperature (LCST). The high adsorption efficiency of Cu ions by PNIPAAm‐MAA polymer particles provides an effective technique for recovering metal ions (e.g., Cu²⁺) from wood treated with metal‐based preservatives. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Supercritical hydrothermal synthesis of titanium dioxide nanostructures with controlled phase and morphology

A novel template- and organic-free synthesis of TiO₂ nanostructures with controlled phase and morphology was realized through batch supercritical hydrothermal treatment (400 °C) of titanate nanotubes (TNTs) with H₂O₂ in NaOH aqueous solution. Well-defined 3D titanate hierarchical spheres (THSs), 2D multilayered titanate nanosheets (TNSs), and 1D monodisperse anatase nanorods (ANRs) exposing (0 1 0) facets were prepared in 15 min by slightly varying the NaOH solution pH. Specifically, the obtained Na/H-THSs (without/with HCl neutralization) exhibited highly porous structures with large specific surface area (109 m² g⁻¹ and 196 m² g⁻¹, respectively). Temperature-dependent phase and morphology evolutions of products under subcritical condition (200 and 300 °C) were investigated. The formation of the TiO₂ nanostructures from TNTs was proposed mainly following a dissolution–nucleation-growth mechanism, suggesting that both supercritical temperature and NaOH solution pH were determinant factors governing the nucleation and growth process and thus the phase and morphology.