Polymeric pH-sensitive membranes—A review

Progress in Polymer Science 36 (2011) 1499–1520

Contents lists available at ScienceDirect

Progress in Polymer

Science

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 /p p o l y s c

Polymeric pH-sensitive membranes—A review

Changsheng Zhao ∗,Shengqiang Nie,Min Tang,Shudong Sun

College of Polymer Science and Engineering,State Key Laboratory of Polymer Materials Engineering,Sichuan University,Chengdu 610065,China

a r t i c l e海蛇头

i n f o

Article history:

奇魅植物酶Received 9September 2010

Received in revised form 29April 2011Accepted 2May 2011

Available online 25 May 2011

Keywords:

pH-sensitive membranes Flat sheet

Hollow-ﬁbre membrane Blending

Surface-modiﬁcation

Membrane pore size change

a b s t r a c t

Signiﬁcant progress has been achieved in recent years in the ﬁeld of pH-sensitive mem-branes.In many cases,pH-sensitive membranes are systems for which the ﬂux,membrane pore size,and solute rejection ratio may be manipulated by changing the pH.This review summarizes recent developments covering the preparation,pH-responsive properties,and applications in various disciplines.The pH-sensitive groups and the evaluation parame-ters for pH-sensitive membranes are reviewed and discussed.A variety of preparation methodologies,including blending,pore-ﬁlling,surfac

e-grafting,and surface-coating tech-niques are described,and some of their salient features are highlighted.The ﬂat-sheet form and hollow-ﬁber form pH-sensitive membranes are reviewed.Membrane pore size change and electroviscous effect are discussed.Furthermore,future perspectives of pH-sensitive membranes are discussed.

Abbreviations:AA,acrylic acid;AAm,acryl amide;AFM,atomic force microscopy;AIBN,2,2 -azo-bisisobutyronitrile;AMPS,2-acrylamido-2-methylpropanesulfonic acid;AOHOBA,4-(6-(acryloyloxy)hexyloxy)benzoic acid;ATRP,atom transfer radical polymerisation;BP,benzophenone;BPO,benzoyl peroxide;CCl 4,carbon tetrachloride;CHCl 3,chloroform;–COOH,carboxyl;DEMA,2-dimethylamino ethyl methacrylate;DG,degree of grafting;DIB,1,4-di-iodobutane;DM,degree of modiﬁcation;DMAC,dimethylacetamide;DMAEMA,2-(dimethylamino)ethyl methacrylate;DMF,dimethylfor-mamide;DMFC,direct methanol fuel cell;DS,dextran sulphate;DVB,divinylbenzene;EB,electron beam;ECA,ethylcellulose;ER,environmentally responsive;GMA,glycidyl methacrylate;HDPE,high-density polyethylene;HOEMA,2-hydroxyethyl methacrylate;HPC,hydroxypropyl cellulose;IEC,ion exchange capacity;IPN,interpenetrating polymer network;i-PP,isotactic polypropylene;i-PrOH,isoprop

anol;LbL,layer-by-layer;LDPE,low-density polyethylene;Lys,lysozyme;MA,methyl acrylate;MAH,maleic anhydride;MBAA,methylene bisacrylamide;MF,microﬁltration;MMA,methyl methacrylate;NF,nanoﬁltration;NIPAAm,N -isopropyl acrylamide;NMP,N -methyl-2-pyrrolidone;Ny,nylon;RO,reverse osmosis;SA,sul-fonate acid;P2VP,poly(2-vinylpyridine);P4VP,poly(4-vinylpyridine);PA,polyamide;PA 6.6,polyamide 6.6;PAA,poly(acrylic acid);PAA–AN,poly(acrylic acid–acrylonitrile);PAH,poly(allylamine hydrochloride);PAN,poly(acrylonitrile);PAN–DMAEMA,poly(acrylonitrile and 2-dimethylamino ethyl methacry-late);P(AN–AA–VP),poly(acrylonitrile–acrylic acid–vinyl pyrrolidone);PEN,polyethylenamine;PC,polycarbonate;PDM,poly(N ,N -dimethylaminoethyl methacrylate);PDMAEMA,poly(N ,N -dimethylaminoethyl methacrylate);PDMS,poly(dimethylsiloxane);PE,polyethylene;PEBAOHOB,1,4-phenylene bis(4-(6-(acryloyloxy)hexyloxy)benzoate);PEI,polyethylenimine;PEGMA,poly(ethylene glycol)methacrylate;PEK-C,cardo polyetherketone;PES,polyethersulfone;PET,polyethylene terephthalate;PMAA,poly(methacrylic acid);PNIPAm,poly(N -isopropylacrylamide);PNIPAm-co-MAA,poly(N -isopropylacrylamide-co-methacrylic acid);PNVCL,poly(N -vinylcaprolactam);PP,polypropylene;POF,polyoleﬁn;PSF,polysulfone;PSS,poly(sodium 4-styrenesulfonate);PTFE,polytetraﬂuoroethylene;PV,pervaporation;PVDF,poly(vinylidene ﬂuoride);qP2

VP,1,4-di-iodobutane;RAFT,reversible addition-fragmentation chain transfer radical polymerisation;R I ,immobilisation ratio;SCCO 2,supercritical carbon dioxide;SSS,sodium p -styrene sul-fonate;St,styrene;tBA,tert-butyl acrylate;TFE–HFPP,tetraﬂuoroethylene–hexaﬂuoropropylene;TDI,toluene-2,4-di-isocyanate;TEPC,track-etched polycarbonate membranes;TPU,thermoplastic polyurethane;UF,ultraﬁltration;UV,ultraviolet;UV-GP,ultraviolet-initiated graft polymerisation;VDF,vinylidene ﬂuoride;VP,vinylpyridine;WSC,water-soluble chitosan.

∗Corresponding author.Tel.:+862885400453;fax:+862885405402.

E-mail addresses:zhaochsh70@scu.edu ,zhaochsh70@163 (C.Zhao).

居里夫人的女儿1500 C.Zhao et al./Progress in Polymer Science36 (2011) 1499–1520

Contents

1.Introduction (1500)

2.Brieﬂy introduction of pH-sensitive membranes (1501)

鱼肝油丸是哪一种维生素

2.1.pH-sensitive groups (1501)

2.2.Evaluation parameters for pH-sensitive membranes (1502)

3.Flat-sheet pH-sensitive membranes (1502)

3.1.Blending pH-sensitive membranes (1503)

3.2.Pore-ﬁlled pH-sensitive membranes (1504)

3.2.1.Preparation and characterization of pore-ﬁlled membranes (1505)

3.2.2.Modelling of pore-ﬁlled membranes (1505)

3.2.3.Application of pH-sensitive pore-ﬁlled membranes (1506)

3.3.Surface-grafting pH-sensitive membranes (1507)

3.3.1.Photo-induced grafting (1507)基尼系数

3.3.2.Thermal-induced grafting (1509)

3.3.3.Ozone-induced grafting (1510)

3.3.4.Grafting in supercritical carbon dioxide (1510)

3.3.5.Plasma-induced grafting polymerisation (1511)

3.3.6.Surface-initiated atom transfer radical polymerisation (1511)

3.3.7.Reversible addition-fragmentation chain transfer radical polymerisation (1511)

3.3.8.Redox-grafting (1512)

3.4.Surface-coating pH-sensitive membranes (1512)

4.Hollowﬁber pH-sensitive membranes (1512)

4.1.Blending pH-sensitive hollowﬁber (1512)

4.2.Pore-ﬁlled pH-sensitive hollowﬁber (1513)

4.3.Surface-grafting pH-sensitive hollowﬁber (1513)

4.4.Surface-coating pH-sensitive hollowﬁber (1514)

ire5.Membrane pore size change and electroviscous effect (1514)

6.Concluding remarks and future perspective (1515)

Acknowledgements (1517)

References (1517)

1.Introduction

Membrane technology has become an important sep-aration technology over the past decades.A principal advantage of membrane technology is that it works with-out the addition of chemicals,has a relatively low energy use and involves easy and well-understood process meth-ods.The term membrane technology is applied to a number of separation processes,each using a membrane but differ-ing in the details of the method.

•Membranes suited for technical applications may be clas-siﬁed by the following characteristics[1,2];•Membrane materials.Organic polymers,inorganic materi-als(oxides,ceramics,metals),mixed matrix or composite materials;

•Membrane cross-section.Isotropic(symmetric),integrally anisotropic(asymmetric),bi-or multilayer,thin-layer or mixed matrix composite;

•Preparation method.Phase separation(phase inversion)of polymers,sol–gel process,interface reaction,stretching, extrusion,track-etching,and micro-fabrication;•Membrane shape.Flat sheet,hollowﬁber,and hollow cap-sule.

Alternatively,membranes may also be divided into artiﬁcial and natural membranes based on their origin. An artiﬁcial,or synthetic,membrane is a synthetically created membrane intended for separation purposes in the laboratory or in industry.Synthetic membranes have been successfully used for small and large-scale industrial processes[3],in artiﬁcial organs and in medical devices for blood puriﬁcation,including haemodialysis,haemodi-aﬁltration,haemoﬁltration,plasmapheresis and plasma collection[4–8].Synthetic membranes can be produced from organic materials,such as polymers and liquids,or from inorganic materials.Most of the commercially uti-lized synthetic membranes in the separation industry and in artiﬁcial organs are made of polymeric materials.

Polymeric membranes are membranes that take the form of polymeric interphases that can selectively trans-fer certain chemical species over others.There are several mechanisms that can be

exploited in their functioning. Knudsen diffusion and solution diffusion are prominent mechanisms.The membranes have advanced or novel functions in various membrane separation processes for liquid and gaseous mixtures(gas separation,RO,PV,NF, UF,and MF)and in other important applications of mem-branes such as biomaterials,catalysis(including fuel cell systems)or lab-on-a-chip technologies[2,9].

To control the permeability and separation performance of membranes,stimuli-responsive membranes have been developed in recent years.Stimuli-responsive(“intelli-gent”)membranes and materials exhibit abrupt property changes in response to small changes in external stimuli such as temperature,pH,ionic and/or solvent composition of the media,concentration of speciﬁc chemical species, the electricﬁeld,and photo-irradiation[10–14].Compared with other external stimuli,pH sensitivity gives more choices both for the materials and for the application envi-

C.Zhao et al./Progress in Polymer Science36 (2011) 1499–15201501

ronment,making it a powerful technique;thus,we focused on pH-responsive membranes in this review.

In recent years,several researchers have reviewed polymeric membranes,some of which cover pH-s

ensitive membranes.Wandera et al.[15]reviewed stimuli-responsive membranes,covering the design of these membranes and their ever-expanding range of use,but there was only one section related to pH-sensitive mem-branes.This section addressed the stimuli-responsive changes in the membrane structure and the surface char-acteristics that enable novel applications.He et al.[16] reviewed the use of photo-irradiation for the preparation, modiﬁcation and stimulation of polymeric membranes.For de novo preparation of membranes from low molar mass or soluble precursors,photo-initiated polymerisation and photo-cross-linking are the main methods,and stimuli-responsive membranes,including pH-sensitive mem-branes(mainlyﬂat-sheet membranes),can be prepared using these methods.Vladimir[17]reviewed multifunc-tional and stimuli-sensitive pharmaceutical nanocarriers. Srinivas et al.[18]reviewed stimuli-responsive nanocar-riers for drug and gene delivery.pH sensitivity was the ﬁrst example of stimuli sensitivity used to modify drug and gene delivery system behaviour in a desired way in the pathological areas with a decreased pH value and held promise as an area for future research.In these systems,pH-sensitive/responsive components were incor-porated/attached to nanocarriers.However,noﬂux control and/or separation performance were concerned in these two reviews.Anna and Marek[19]reviewed stimuli-responsive macromolecules and polymeric coatings,and the potential emerging applications in medicine,phar-macology,nanotechnology,biomaterials,or otherﬁelds of materials science and materials engineering

of these “smart”macromolecules were discussed.The stimuli-responsive characteristics described in the review focus on physical and chemical stimuli that result in numer-ous responses leading to unique behaviours in complex environments.Shao and Huang[20]reviewed polymeric membrane PV.This review provided an analytical overview of the potential of PV for separating liquid mixtures in terms of the solubility parameter and the kinetic parameter of solvents.The fundamental properties of the membrane were the primary focus;the preparation of membranes was not emphasized,and pH-sensitivity was not mentioned.

In contrast to other reviews for polymeric mem-branes,which are usually classiﬁed as a functionality of the membranes,this review classiﬁed the morphology of pH-sensitive membranes based on the two different membrane shapes,ﬂat-sheet and hollow-ﬁber membranes. It is well known that membranes are usually intended for separation purposes in the laboratory or in industry, and membranes have been successfully used for small-and large-scale industrial processes since the middle of twentieth century.For industrial processes,hollow-ﬁber membranes are believed to be more effective and cheaper thanﬂat-sheet membranes because the surface/volume ratio of hollow-ﬁber membranes is larger and because very few suppliers supplyﬂat-sheet membranes.Clas-sifying based on the morphology of the pH-sensitive membranes may bring more attention to the use of me

m-branes for separation purposes and industrial processes. Of course,drug and gene delivery are important applica-tions of pH-sensitive macromolecules,polymeric coatings and nanocarriers;the morphology and preparation method of these pH-sensitive macromolecules,nevertheless,are different from those of materials used for separation and industrial processes.

The main part of this review is organized accord-ing to the two different pH-sensitive membrane shapes,ﬂat-sheet and hollow-ﬁber membrane.Forﬂat-sheet pH-sensitive membranes,the membrane preparation methods are discussed(Section3).For hollow-ﬁber pH-sensitive membranes,the preparation methods,mainly related to our experimental results,are also discussed(Section4).To analyse the mechanisms responsible for the pH sensitivity, the membrane pore size change and electroviscous effect on the sensitivity are discussed(Section5).The conclusion includes a brief outlook towards possible new develop-ments in this interesting area(Section6).However,due to the diversity of theﬁeld,selections had to be made that reﬂect the particular interests of the author.

2.Brieﬂy introduction of pH-sensitive membranes

In principle,pH-sensitive membranes can be divided into non-porous and porous membranes(or membranes with changing charge).However,the ultimate effect of the pH-responsive change on me

mbrane properties will depend primarily on the barrier itself[16].For non-porous membranes,a change in swelling of the barrier can lead to a change in the permeability and selectivity.For porous membranes,layers of tailored grafted functional polymers (with pH-sensitive groups)on the pore walls can be used to reversibly change the permeability and/or selectivity of the membrane.The most straightforward mechanism is the alteration of the effective pore diameter via a change in the conformation of a grafted polymer as a function of a solution’s pH.For both of the membranes,conformational changes can be triggered by pH-responsive groups(such as carboxyl,pyridine,imidazole,and dibuthylamine groups [21,22])or the units in the bulk of the membrane material; their modiﬁed structure causes changes in solvent uptake. The pH-responsive binding or release to or from functional groups on the outer or pore surface of a membrane can inﬂuence the adsorption(fouling)properties,but can also be used to construct membrane adsorbers[16,23].

2.1.pH-sensitive groups

The most commonly used pH-responsive functional groups are carboxyl and pyridine groups.A carboxyl group (or carboxy)is a functional group consisting of a carbonyl and a hydroxyl,having the chemical formula–C(O)OH, which is usually written as–COOH or–CO2H.At low pH, carboxyl groups

are protonated and hydrophobic inter-actions dominate,leading to a volume shrinkage of the polymer that contains the carboxyl groups.At high pH, carboxyl groups dissociate into carboxylate ions,resulting in high charge density in the polymer,causing it to swell. Based on the conﬁgurational change of the polymer,the membrane pore size can be adjusted,resulting in regula-

1502 C.Zhao et al./Progress in Polymer Science36 (2011) 1499–1520

tion of the solution permeability and solute rejection.The chain conﬁguration of weak polyacid is a function of the p K a of the polymer.The p K a of PAA in solution is approxi-mately4.3–4.9,depending upon the measurement method [24].Another widely used material is PMAA[25].SA groups also show pH-sensitivity,but are seldom used.

In contrast to the alkali-swellable carboxyl group, pyridine is an acid-swellable group.Under acidic envi-ronmental conditions,the pyridine groups are protonated, giving rise to internal charge repulsions between neigh-bouring protonated pyridine groups.Charge repulsion leads to an expansion in the overall dimensions of the polymer containing the groups.At higher pH values,the groups become less ionised,the charge repulsion is reduced and the polymer–polymer interactions increase,leading to a reduction of the overall hydrodynamic diameter of the polymer[26,27].The most

widely used polymer con-taining pyridine is poly(vinyl pyridine),which is based on basic monomers,such as4-vinylpyridine(4VP),2-vinylpyridine(2VP).The p K a of poly(vinyl pyridine)in solution is approximately3.5–4.5,depending on the mea-surement method and its form[28–30].Other pH-sensitive functional groups,such as imidazole,dibuthylamine and tertiary amine methacrylates have also been investigated [17,22,31].These groups are also cationic groups and are acid-swellable.

2.2.Evaluation parameters for pH-sensitive membranes

To evaluate a pH-sensitive membrane,parameters such as membrane IEC,membrane waterﬂux as a function of pH, membrane pH reversibility,permeability control of solu-tions,and rejection of solutes are usually investigated.

The charge property of a pH-sensitive membrane can be expressed in terms of membrane IEC.The IEC of a membrane can be calculated based on the mass of the anion or the cation groups and is termed theoretical IEC. In contrast,titrated IEC is measured by titrating by stan-dard NaOH solution or HCl solution.Titrated IEC is always lower than theoretical IEC,owing to the fact that the pH-sensitive groups are incorporated in,or grafted on,the membrane,and the degree of the dissociation

of the groups is thus less than100%.In general,the larger the IEC,the larger is the dependence of solution permeability on pH. The IEC of the reported commercial ion exchange mem-branes is near1–2mequiv./g[32].However,the IEC of the reported pH-sensitive membranes ranges from0.01to sev-eral mequiv./g.If the pH-sensitive membrane has a larger IEC,the membrane can also be used as an ion exchange membrane.

By measuring the membrane waterﬂux as a function of pH,the pH chemical valve behaviour for the mem-brane can be obtained.For the pH-sensitivity experiment, the pH value of the feed solution was adjusted by adding HCl or NaOH solution.The pH dependence of theﬂux was then determined at pH values ranging from acidic to basic,in random sequence.For membranes modiﬁed by alkali-swellable groups(such as carboxyl),theﬂux decreased with increasing pH,while it increased for the membranes modiﬁed by acid-swellable groups(such as pyridine).

Membrane pH reversibility is another parameter used to evaluate a pH-sensitive membrane.The pH reversibility refers to the reversible change of the polymer conformation or the reversible pore size change inside the membrane and reﬂects the swelling-shrinkage behaviour of the polymer containing the pH-sensitive groups.For the pH reversibility experiment,the aqueous solution was introduced into the membraneﬁlter by a pump with a controlledﬂow rate.The ﬁlter was alternatively fe

d with HCl and NaOH solutions at constant pressure with short double distilled water rinsing between.

Control of solution permeability is achieved by chang-ing the pH of the solution.The rejection ratio(or sieving coefﬁcient)of a solute changes with a change in the pH of the solution during theﬁltration process,dictated primar-ily by the change in the membrane pore size.In addition, the electroviscous effect modiﬁes the rejection ratio,due to the membrane charge.

3.Flat-sheet pH-sensitive membranes

Flat-sheet pH sensitive membranes are widely inves-tigated since theﬂat-sheet membrane is easy to prepare and fabricating the device is simple.For the membranes, pH-sensitive groups or polymers(or polyelectrolytes) should be contained.Polyelectrolytes can be directly used to prepareﬂat-sheet pH-sensitive membranes.Su and Li[33]prepared a weak polyelectrolyte UF membrane based on poly(acrylonitrile and2-dimethylamino ethyl methacrylate)(PAN–DMAEMA)copolymer by phase inver-sion in a wet process.The PAN–DMAEMA membrane had the typical asymmetric structure.The waterﬂux of the PAN–DMAEMA UF membrane was tunable due to the switch of the stretched and collapsed states of PDMAEMA chains at different pH values and NaCl con-centrations in the feed sol

ution.However,the waterﬂux of PAN–DMAEMA membrane could not reversibly recover its originalﬂux after environmental stimuli,perhaps due to residual exchanged-ions and ionic pairs disturbing the ability of the PDMAEMA in the skin layer of ultraﬁltration membrane to switch conformation.A multi-responsive bio-polyelectrolyte membrane(alginate gel membrane) was also prepared by Gopishetty et al.[34].The perme-ability,adhesiveness and mechanical properties of the membrane could be regulated by the pH and ionic strength of the surrounding aqueous solutions.

It was difﬁcult to recover the original waterﬂux for pH-sensitive membranes prepared directly by weak poly-electrolyte after environmental stimuli.Furthermore,the strength of the polyelectrolyte membrane is always very low.Thus,pH-sensitive membranes are usually prepared as follows:the pH-sensitive groups or polymers are incor-porated in the membrane matrix(blended),grafted(or coated)on the membrane surface or membrane pore sur-face,orﬁlled into the membrane pores(Fig.1).Only the pH-sensitive groups on the membrane surface or on the surfaces of the membrane pores can participate in pH-responsive activities,even if the pH-sensitive groups or polyelectrolytes are incorporated throughout the entire membrane matrix.

C.Zhao et al./Progress in Polymer Science36 (2011) 1499–1520

1503

In1986,Osada et al.[25]prepared stimuli-responsive composite membranes consisting of a porous substrate onto which PMAA was grafted.They found that the water permeability was very sensitive to pH:in some cases per-meability changed by three orders of magnitude when the membrane was introduced to changes in pH or ionic strength,or to the addition of di-and trivalent metal ions such as Cu2+and Cr3+.The enhanced permeation of water through the PMAA-grafted membranes was caused by mechanochemically induced conformational changes of the PMAA chains,which increased the apparent size of the micropores in the membrane.

Mika et al.[35]fabricated a new type of membrane composed of a MF substrate and a pore-ﬁlling pol

yelec-trolyte by UV induced grafting of4-vinylpyridine onto PE and PP MF membranes.The membranes showed out-standing sensitivity to pH and had the capability to reject small inorganic ions in the process of RO.In recent years, there has been a rapidly increasing interest in membranes with reversible pH“switchable”properties[36–40].Due to the practically unlimited possibilities to design func-tional macromolecular systems,pH-responsive polymers are the most important materials for such“smart”mem-branes.Many methods to prepare pH sensitive membranes have been provided,and these will be discussed in detail in the following sections.

3.1.Blending pH-sensitive membranes

The simplest but most important method to prepare pH-sensitive membranes is the blending method.Nam and Lee[41]prepared PV membranes consisting of chi-tosan(as a cationic polyelectrolyte)and PAA(as an anionic species)by blending two polymer solutions in different ratios.An increase of PAA content in the polyelectrolyte complex membranes affected the swelling behaviour and PV performance of the water–ethanol mixture.Ahmad et al.[42]prepared polymericﬁlms of varying crosslinking densities and of different molar concentrations from the epoxidized oil/diglycedyl ether of bis-phenol A(DGEBA) epoxy/polyamide/starch by blending at ambient temper-ature.The polymericﬁlms showed a typical pH and temperature response:at low pH

and low temperature, membrane swelling was at a maximum,whereas at high pH and high temperature,the membrane exhibited complete deswelling.

M’Bareck et al.[43]reported a simpliﬁed,efﬁcient and economical method for fabricating ion exchange UF mem-branes.To obtain these membranes by phase inversion method,PSF and PAA were each separately dissolved in DMF,and the two solutions were mixed in the desired pro-portions.The blended PSF/PAA UF membranes could be used for the removal of certain heavy metals from water.Rejection of lead,cadmium and chromium was high,up to100%at a pH higher than5.7.Rejection efﬁciency cor-respondingly decreased at low pH[44].However,some of the PAA was eluted during the preparation process, and this could be observed by monitoring the immobil-isation ratio(R I)of PAA,which is deﬁned as the ratio of the actual IEC to the theoretical IEC,as shown in Fig.2.Zhang et al.[45]developed pH and temperature sensitive membranes by blending ECA with nanoparti-cles of poly(N-isopropylacrylamide-co-methacrylic acid). The nanoparticles were synthesized by aqueous disper-sion polymerisation.In this process,the nanoparticles were puriﬁed by membrane dialysis and dried before blending in the membranes.To avoid the leakage of the nanoparticles from the composite membrane surface,the membranes were coated with polyelectrolyte layers.

In the work mentioned above,the swelling perfor-mance of the membranes was investigated intensively,but the permeability of the membranes as a function of pH was not discussed in detail.Zhai[46]prepared a copoly-mer of PVDF-g-P4VP through the graft copolymerisation of PVDF with4VP.Through the blending of PVDF-g-P4VP copolymer with poly PNIPAm in an NMP solution,PVDF-g-P4VP/PNIPAm MF membranes were fabricated by phase inversion in aqueous media.Theﬂux of aqueous solu-tions through the blend membranes exhibited pH-and temperature-dependent behaviour,Fig.3.As shown in the ﬁgure,the PVDF-g-P4VP/PNIPAm blend membranes exhib-ited an increase in the permeation rate in response to the increase in the permeate temperature.The temperature-dependent permeation rate was caused by the change in the conformation of the PNIPAm polymer on the

mem-Fig.2.Immobilisation ratio(R I)of PAA as a function of the initial blend composition[PAA/(PSF+PAA)]in the casting dope.The membranes were obtained by coagulation,in w

本文发布于:2024-09-21 12:36:50，感谢您对本站的认可！

本文链接：https://www.17tex.com/xueshu/403552.html

上一篇：纺织英语词汇中英文对照系列

下一篇：常用有机基团英文简写

标签：

留言与评论（共有 0 条评论）