Colloids and Surfaces A:Physicochem.Eng.Aspects 396 (2012) 328–335
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Colloids and Surfaces A:Physicochemical and
Engineering
Aspects电脑如何设置锁屏时间
j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c o l s u r f
a
Preparation and characterization of nano-SiO 2/fluorinated polyacrylate composite latex via nano-SiO 2/acrylate dispersion
Fuchun Zhao a ,b ,Xingrong Zeng a ,∗,Hongqiang Li a ,Jing Zhang a
a
College of Materials Science and Engineering,South China University of Technology,Guangzhou 510640,China
b
Key Laboratory of Ministry of Education for Application Technology of Chemical Materials in Hainan
Superior Resources,School of Materials and Chemical Engineering,Hainan University,Haikou 570228,China
a r t i c l e
i n f o
Article history:
Received 1June 2011Received in revid form 13December 2011
Accepted 4January 2012
Available online 12 January 2012
Keywords:Nano-SiO 2
Fluorinated polyacrylate Hydrophobicity
Semi-continuous emulsion polymerization
a b s t r a c t
The organic nano-SiO 2/acrylate dispersion in which methyl methacrylate (MMA)and butyl acrylate (BA)in the micelles act as dispersing media of nano-SiO 2was prepared by sol–gel method with tetraethyl orthosilicate (TEOS)as precursor,hydrochloric acid as catalyst and methacryloylpropyl trimethoxysi-lane (MPS)as modifier.Subquently,the nano-SiO 2/fluorinated polyacrylate composite latex was synthesized by two-stage mi-continuous starved emulsion polymerization bad on the organic nano-SiO 2/acrylate dispersion.The SiO 2/fluorinated polyacrylate composite latex and the resultant films were characterized by Fourier transform infrared spectroscopy (FTIR),dynamic light scattering (DLS),Zeta potential (),angle-resolved X-ray photoelectron spectroscopy (AR-XPS)and contact angle measure-ments (CA).The nano-SiO 2/fluorinated polyacrylate composite latex possd very narrow particle size distributions and good latex stability.Fluorinated groups had a strong tendency to migrate to film sur-face and the surface hydrophobicity of the resultant films was remarkably improved.The mass ratio of methyl methacrylate to butyl acrylate (MMA/BA)has an important influence on the hydrophobicity of the composite films.When the content of dodecafluoroheptyl methacrylate (DFHMA)was 6wt%and the mass ratio of MMA/BA was 1/3,the water contact angle could reach 121◦.The possible mechanism of migration and enrichment of fluorinated groups to the film surface under different MMA/BA mass ratio was propod.
© 2012 Elvier B.V. All rights rerved.
1.Introduction
In recent years,due to unique features including excellent mechanical,optical,electrical,hydrophobicity,thermal stability and flame retardant property [1–3],organic–inorganic composite materials have attracted a great deal of attention and been applied to many fields such as membranes,functional smart coatings,fuel and solar cells,catalysts.Among the organic components,fluori-nated polymers are particularly appealing candidates in terms of their liquid repellence,chemical inertness,low coefficient of fric-tion and good biocompatibility [4]and have been ud in specialty coatings,biomaterial coatings and bionsors,fire retardant coat-ings,microelectronic devices and protection of historic monuments [5–8].At the same time,many kinds of nanoparticles such as SiO 2,TiO 2,Al 2O 3,ZrO 2and CaCO 3[9–13]are ud to fabricate nanocom-posites.Among them,SiO 2is favorable to improve the mechanical property,thermal stability,rin-resistance and perdurability of organic polymers,and most widely ud [14–16].
∗Corresponding author.Tel.:+862087114248;fax:+862087114248.E-mail address: (X.Zeng).
Thus,the type of promising composite material with excellent comprehensive performance is expecte
d to be obtained by incor-porating SiO 2particles into fluorinated polymers.If the inorganic particles finely disper into the polymeric matrix,the hardness,scratch-resistance,impact resistance,and optical properties of the resultant composites may be significantly improved.
Nowadays,SiO 2/fluorinated polymers composites are mainly prepared by two strategies.The simple one is to blend commercial SiO 2or hydrolyzed SiO 2with organic solution of fluorinated poly-mers or aqueous fluorinated latex.For example,superhydrophobic coatings had been prepared by simple mixing of SiO 2with the solution of fluorinated polymers in chloroform solvent [17].Silica-containing fluoroacrylate copolymer latex was synthesized by hydrolysis of tetraethyl orthosilicate in the fluorinated copolymer latex [18].The composite films showed favorable mechanical,opti-cal,water-resistant properties in about 30wt%DFHMA.However,organic solvent was unfriendly and the interaction between nano-SiO 2and core–shell latex was weak in the methods.Another eco-friendly strategy to synthesize SiO 2/fluorinated polymers is by emulsion polymerization in the prence of nano-SiO 2.There have been veral reports on SiO 2/fluorinated polyacrylate nanocom-posite latex [15,19–23].For instance,to strengthen interactions
0927-7757/$–e front matter © 2012 Elvier B.V. All rights rerved.doi:10.lsurfa.2012.01.017
森林防火的作文F.Zhao et al./Colloids and Surfaces A:Physicochem.Eng.Aspects396 (2012) 328–335329
between polymer and silica,nano-SiO2/poly(MMA-co-BA-co-FA) hybrid emulsion was prepared via emulsion polymerization in the prence of MPS-grafted nano-SiO2.Asfluorinated monomer was 15wt%and SiO2was2wt%,the water contact angle could reach 105.4◦[15,24].The superhydrophobic surfaces can be prepared by emulsion polymerization utilizing nano-SiO2(50%mass ratio of monomers)[19]or DFHMA(40wt%bad on total monomers) [20].Moreover,core–shell SiO2/fluorinated polyacrylate nanocom-posite latex particles containingfluorine in the shell were prepared by eded emulsion polymerization using nano-SiO2modified by vinyltriethoxysilicone.The compositefilms showed high contact angle of112.3◦,when the content of DFHMA and nano-SiO2was 34.8wt%and5wt%,respectively[23].
In the above eco-friendly strategy[19–21,23],the introduc-tion procedure of nano-SiO2into composite latex particles ems more complicated.The nano-SiO2wasfirstly prepared through well-known Stöber method,in which large amount of absolute ethanol was ud as reaction medium.Then,the ethanol solvent need to be removed and the silica must be re-disperd in water before polymerization due to the adver effect of large amount of ethanol solvent on polymerization stability,etc.However,the subquent purifying procedure of nano-SiO2through evaporation under re
duced pressure[19–21]or centrifugation[23]may lead to the aggregation of nano-SiO2particles.The aggregated nano-SiO2 is often difficult to be re-disperd and the uniform dispersion of nano-SiO2in the composite latex particle and the resultant com-positefilm is adverly affected.
In addition,for the integration of inorganic particles into trans-parent polymers,not only particle size control is important,but also the particles need to be parated from each other in the com-posites,as aggregates lead to turbidity to increa the haze and to decrea the transmittance of the composites[25].Thus,it is highly desirable to make particle disper in polymer matrix,especially for transparent materials.If,however,the particles form in a disper-sion that the surrounding oil pha is itlf a monomer,the isolation process is redundant.To date,very little work has been done to prepare nano-SiO2/fluorinated polyacrylate composite latex using nano-SiO2/acrylate dispersion in which acrylate monomers act as dispersing media of nano-SiO2.
In the prent work,the oil pha of the acrylate monomers, tetraethyl orthosilicate and methacryloylpropyl trimethoxysilane wasfirstly pre-emulsified to form oil in water emulsion.After the precursor in the micelles was hydrolyzed catalyzed by hydrochlo-ric acid and modified by methacryloylpropyl trimethoxysilane,the organically modified nano-SiO2disperd in acrylate monomers namely as nano-SiO2/acrylate dispersion was prepared.Then,the eded latex was prep
ared via the nano-SiO2/acrylate dispersion by in situ emulsion polymerization and the composite latex particle subquently by mi-continuous eded emulsion polymeriza-tion.The nano-SiO2/fluorinated polyacrylate composite latex par-ticles and the compositefilms were characterized by Fourier trans-form infrared spectrometry(FTIR),the particle size distribution and the latex stability were determined by dynamic light scattering (DLS)and Zeta potential(),respectively.The chemical compo-sitions and hydrophobicity of the compositefilms were analyzed by angle-resolved X-ray photoelectron spectroscopy(AR-XPS)and contact angle measurements(CA).In addition,the effects offluori-nated acrylate monomer content and main monomer ratio on the surface hydrophobicity of compositefilms were investigated.
2.Experimental
半山腰的风景2.1.Materials
裸导线Methyl methacrylate(MMA,A.R.),Butyl acrylate(BA,A.R.) and acrylic acid(AA,99.5%)were obtained from Tianjin
Fuchen
Fig.1.Chemical structure of DFHMA(a),MPS(b)and DNS-86(c). Chemical Reagent Factory,China.Thefluorinated acrylic monomer, dodecafluoroheptyl methacrylate(DFHMA,96%),shown in Fig.1(a), was supplied by Harbin Xeogia Fluorine-Silicon Chemical Co., Ltd.,China.Tetraethyl orthosilicate(Si(OC2H5)4,TEOS, A.R.) were acquired from Tianjin No.1Chemical Reagent Factory, China.Methacryloylpropyl trimethoxysilane(MPS,A.R.)shown
in Fig.1(b)was purchad from GE Co.,Ltd.,USA.The reac-tive anionic emulsifier of ammonium1-propenyloxy-3-(4-nonyl phenol)-2-propanol polyoxyethylene(10)sulfate(DNS-86,98%), shown in Fig.1(c),was provided by Qingxin Hanerchem Chem-ical Technology Co.,Ltd.,China.Potassium persulfate(KPS, A. R.),hydrochloric acid,ethanol and acetone were purchad from Guangdong Guanghua Chemical Factory.Deionized water was ud throughout the experiments.All reagents were ud as received without further purification.
2.2.Preparation of the organic nano-SiO2/acrylate dispersion
The organic nano-SiO2/acrylate dispersion was prepared by sol–gel method with TEOS as precursor,hydrochloric acid as cat-alyst and methacryloylpropyl trimethoxysilane(MPS)as modifier. Firstly,the oil pha mixture of MMA(15.0g),BA(15.0g),TEOS (7.6g)and MPS(0.9g)were introduced into30.0g water solution of DNS-86(1.8g)and hydrochloric acid(0.1g)under vigorously stirring.Then the pre-emulsion was under magnetic agitation at room temperature for24h to generate organic nano-SiO2parti-cles disperd in the acrylate micelles.The3-(methacryloxy)propyl functionalized nano-SiO2/acrylate dispersion was ud for prepar-ing the ed latex.
2.3.Synthesis of the nano-SiO2/fluorinated polyacrylate
composite latex
The nano-SiO2/fluorinated polyacrylate composite latex was prepared in two-stage eded mi-continuous starved emul-sion polymerization process.At thefirst stage,the nano-SiO2/polyacrylate composite ed latex was synthesized by the organic nano-SiO2/acrylate dispersion prepared above.At the c-ond stage,the nano-SiO2/fluorinated polyacrylate composite latex was synthesized by introducingfluorinated acrylate.The emul-sion polymerization was carried out in a250-mL,four-necked, glassflaskfitted with reflux condenr,crescent Teflon mechan-ical stirrer and feeding inlets.A typical synthesis procedure was as follows:firstly,when water bath was heated to75◦C,the one-third of nano-SiO2/acrylate dispersion and an aqueous solution(5.0g)of KPS(0.108g)were added to theflaskfilled with water(80g)and the reaction was lasted for0.5h.The residual nano-SiO2/acrylate dispersion and an aqueous solution(10g)of KPS(0.168g)were introduced into the reactor within2.5h and remained for another 1h.Secondly,the pre-emulsified emulsion consisting of MMA (5.0g),n-BA(5.0g),DFHMA(2.4g),DNS-86(0.6g)and water and
330 F.Zhao et al./Colloids and Surfaces A:Physicochem.Eng.Aspects 396 (2012) 328–
335
Fig.2.Schematic illustration for the formation of SiO 2/fluorinated polyacrylate composite latex particles.
an aqueous solution (5.0g)of KPS (0.050g)were simultaneously dropped into the reactor under starved feed conditions using a dual syringe pump (HL-2N,Huxi Analytical instruments Co.,Ltd.,Shanghai,China)in about 3h.At last,the reaction media was heated to 80◦C and kept stirring for another 1.5h to yield stable nano-SiO 2/fluorinated polyacrylate composite latex.The synthe-sis of the SiO 2/fluorinated polyacrylate composite latex particles is prented in Fig.2.
The resultant films were prepared from the composite latex spread on cleaned glass substrate and allowed to dry at room tem-perature for 5days or under vacuum at 100◦C for 12h.The film thickness measured was ca.15m.
2.4.Measurements
Fourier transform infrared (FTIR)spectra were recorded on a Tensor 27Spectrometer (Bruker Optics,Germany).The measure-ments were carried out in the range of 4000–400cm −1.The number of scans per spectrum was 32,and the spectral resolution was 4cm −1.SiO 2for detection was obtained by using centrifugation-redispersion elution cycles to remove unreacted MPS and acrylate monomers.
The particle size and its distributions of nano-SiO 2/fluorinated polyacrylate composite latex particles were determined by dynamic light scattering (DLS)on a Particle Size Analyzer (90plus,Brookhaven Instruments Corporation).The composite latex par-ticles were highly diluted (C <0.01wt%)before testing to prevent multiple scattering.
The Zeta potentials of composite latex were determined on a Zetasir Nano instrument (Malvern Instruments Ltd.).The com-posite latex particles were diluted with deionized water into an appropriate concentration and the pH was adjusted to six.
The water contact angles were measured using contact angle goniometer (JC2000C,Shanghai Powereach Company,China)at room temperature.Static contact angles were obtained from 5L droplet of deionized water ttled on the surface of SiO 2/fluorinated polyacrylate composite films.More than five contact angles on the different site of the film were averaged to get a reliable value for each sample.
The composite latex films were analyzed by X-ray photoelectron spectroscopy (XPS)(Axis Ultra DLD ,Kratos,Ltd.,UK),equipped with Al K ␣(1486.7eV)X-ray source.All sample films were outgasd before analysis for 12h under ultra-high vacuum (<1.3×10−6Pa).
我就慢慢地The transmittance and haze of the films were measured on Photoelectric Hazemeter (WGW,Shanghai Precision &Scien-tific Instrument Co.,Ltd.)by standard test method according to GB2410-80.
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3.Results and discussion
3.1.FTIR
Fig.3shows the FTIR spectra of SiO 2(a),MPS (b)and MPS modi-fied SiO 2(c).In the spectrum (a)and (c),the symmetrical stretching vibration of Si O Si at 1080cm −1appears and it is the character-istic peak of SiO 2particles [24].The spectrum (c)appears peaks of the stretching vibration of C H at 2955cm −1,C O at 1720cm −1and C C at 1639cm −1,indicating that SiO 2was successfully modi-fied by MPS.In spectrum (c),the relative intensity of the adsorption at 3340cm −1corresponded to OH on the surface of SiO 2is much weaker than that of spectrum (a),indicating that MPS had grafted on the surface of SiO 2by condensation between OH on the sur-face of SiO 2and OH that was from the hydrolysis of OCH 3of MPS moieties.
Fig.4shows the FTIR spectra of poly(MMA-co-BA)com-posite film (a),nano-SiO 2/poly(MMA-co-BA)composite film (b),poly(MMA-co-BA-co-DFHMA)composite film (c)and nano-SiO 2/poly(MMA-co-BA-co-DFHMA)composite film (d).The charac-teristic absorption of C C bond at 1639cm −1disappears,indicating that all monomers have taken part in copolymerization.The peak of Si O Si bending vibration at 474cm −1[15]appears in the spectrum (b)and (d),further confirming that nano-SiO 2was in situ-generated in the composite latex.Spectrum (c)and (d)
show
Fig.3.FTIR spectra of SiO 2(a),MPS (b)and MPS modified SiO 2(c).
F.Zhao et al./Colloids and Surfaces A:Physicochem.Eng.Aspects396 (2012) 328–335
331
Fig.4.FTIR spectra of poly(MMA-co-BA)film(a),SiO2/poly(MMA-co-BA)composite film(b),poly(MMA-co-BA-co-DFHMA)compositefilm(c)and SiO2/poly(MMA-co-BA-co-DFHMA)compositefilm(d).
new peaks of C F stretching vibration at1303cm−1and wag-ging vibration at691cm−1[23,26],which indicates that DFHMA had taken part in the copolymerization and resulted in formation of poly(MMA-co-BA-co-DFHMA)and SiO2/poly(MMA-co-BA-co-DFHMA)latex.At the same time,a broader adsorption band of1050–1310cm−1showed in spectrum(d),which is resulted from stretching vibration of Si O at1070–1110cm−1,overlap-ping with stretching vibration and wagging vibration of C F at1110–1289cm−1,confirms thatfluorinated acrylate monomer DFHMA can be copolymerized into the latex particles as desired through two-stage eded mi-continuous starved emulsion poly-merization.3.2.Particle size and distributions
Fig.5shows the particle size and its distributions of pure poly-acrylate particles(a),nano-SiO2containing polyacrylate particles
(b)and nano-SiO2containingfluorinated polyacrylate particles
(c).As can be en from Fig.5,the average diameter of pure polyacrylate particles(a)is111.8nm,and tho of nano-SiO2 containing polyacrylate particles(b)and nano-SiO2containing fluorinated polyacrylate particles(c)increa to122.1nm and 130.5nm,respectively.The polydispersity index of the particles widens a little from0.015to0.084.However,the polydispersity indices of the particles are all less than0.084,indicating that the dis-tribution of resultant particles is monomodal.The narrow particle size distributions and the growth in particle sizes of the com-posite particles suggest that most of in situ-generated nano-SiO2 are encapsulated into polyacrylate andfluorinated polyacrylate latex particles.A small amount of particles with smaller size than pure polyacrylate latex particles is obrved in(c),which can be explained that free unmodified nano-SiO2is not encapsulated. 3.3.Effect of emulsifier content on stability of the composite latex
Zeta potential is a very good index of the magnitude of the interaction between colloidal particles and commonly ud to asss the stability of colloidal systems.The general dividing line between stable and unstable suspensions is generally taken at either+30or−30mV[27].Particles with Zeta potentials more positive than+30mV or more negative than−30mV are normally considered stable.The Zeta potential of nano-SiO2/fluorinated composite latex particles with an increasing content of DNS-86 was investigated.Table1and Fig.6show that the Zeta potential of nano-SiO2containingfluorinated pol
yacrylate latex particles are more negative than−30mV when the content of DSN-86ranges from6to11wt%,indicating that composite latex particles are sta-ble.The Zeta potential decreas from−33.4mV to−48.2mV
with Fig.5.Particle size and its distributions of poly(MMA-co-BA)composite particles(a),nano-SiO2/poly(MMA-co-BA)composite particles(b),nano-SiO2/poly(MMA-co-BA-co-DFHMA)composite particles(c).(a)0wt%SiO2and0wt%DFHMA;(b)5.5wt%SiO2and0wt%DFHMA;and(c)5.5wt%SiO2and6wt%DFHMA.
332 F.Zhao et al./Colloids and Surfaces A:Physicochem.Eng.Aspects 396 (2012) 328–335
Table 1
Zeta potential of SiO 2/fluorinated composite latex.
DNS-86content (wt%)a 67891011Mean Zeta potential (mV)
−33.4
−48.2
−44.3
−45.7
−40.5
−41.8
a
DNS-86was bad on the total weight of MMA and
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Fig.6.Zeta potential of SiO 2/fluorinated composite latex with different content of DNS-86:(a)6wt%,(b)7wt%,(c)8wt%,(d)9wt%,(e)10wt%,and (f)11wt%.
the content of DSN-86up to 7wt%,after which it begin to increa and finally remain relatively constant.DNS-86is a kind of reactive anionic surfactant that has negative charge.At low content,the incread molecules of DNS-86are mainly anchored to the com-posite particle surface,resulting in a decrea in Zeta potential.At high concentration of DNS-86,the smaller size micelle would form the smaller size particle,which has less negative charge anchored to per particle and makes the Zeta potential increa.In that ca,further increa in DNS-86will not make Zeta potential decrea once the particle surface is saturated by surfactant,thus leading to a relative constant.The results demonstrate that the Zeta potential distribution is a monomodal distribution,which is in accordance with the result of DLS analysis.
3.4.Hydrophobicity
Water contact angle is commonly ud as a criterion for the evaluation of hydrophobicity of a solid surface [28].Water contact angle (Â)usually describes the hydrophobic behavior of surface.The surface is hydrophobic when Âis higher than 90◦and the sur-face is hydrophilic when Âis lower than 90◦[29].The water contact angles of SiO 2/poly(MMA-co-BA-co-DFHMA)composite films with different content of SiO 2and DFHMA are showed in Fig.7.The results show that the water contact angle incread from 71.0◦to 100.1◦with incorporation of SiO 2into the composite film
and
Fig.7.Water contact angle of SiO 2/poly(MMA-co-BA-co-DFHMA)composite films with different content of SiO 2and DFHMA.The major tick labels of abscissa axis is in the form of A/B,where A and B denote the mass fraction of SiO 2and DFHMA respec-tively.For all the film samples,MMA/BA mass ratio equaled 3/1and the content of SiO 2and DFHMA are bad on total mass of MMA and BA.
