Resent researches and development in the field of membrane science are focused on improvement of synthetic membranes’ functionality. Combination of soft polymer pH- and temperature-sensitive hydrogels with rigid ultrafiltration membrane attracts much interest as a new class of smart functional systems. In this research we develop pH- and temperature-sensitive composite membranes using radical copolymerization method and study their properties depending on hydrogel composition, nature of synthetic mem-branes, temperature and pH of external medium.
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Burban, A.F.

Konovalova, V.V.

Pobigay, G.A.

Samchenko, Y.M.

Ulberg, Z.R.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 2 No 2, 02FNC15(3pp) (2013)   2304-1862/2013/2(2)02FNC15(3) 02FNC15-1  2013 Sumy State University Nanocomposite Membranes with pH- and Thermo-sensitive Function  V.V. Konovalova1, G.A. Pobigay1, Yu.M. Samchenko2, A.F. Burban1, Z.R. Ulberg2  1 National University of Kiev-Mohyla Academy, 2, Skovorody Str., 04655 Kiev, Ukraine 2 Insitute of Biocolloid Chemistry, 47, Vernadsky Ave., Kiev, Ukraine  (Received 07 June 2013; published online 01 September 2013)  Resent researches and development in the field of membrane science are focused on improvement of synthetic membranes’ functionality. Combination of soft polymer pH- and temperature-sensitive hydrogels with rigid ultrafiltration membrane attracts much interest as a new class of smart functional systems. In this research we develop pH- and temperature-sensitive composite membranes using radical copolymeriza-tion method and study their properties depending on hydrogel composition, nature of synthetic mem-branes, temperature and pH of external medium.  Keywords: Membrane, Hydrogel, Swelling, pH-, Thermo-sensitivity, Phase transition.   PACS number: 68.55.–a    1. INTRODUCTION  The so-called “smart” systems that tend to copy functioning of living organisms and natural formations responding to environmental factors by changing their physico-chemical surface characteristics, i.e. sorbabil-ity, swelling ability, permeability, surface activity and selectivity, optical characteristics are in the focus of attention of investigators. Ionic strength, illumination ability, change of electrical and magnetic fields are outer factors that experimentally influence the above- mentioned systems [1].  Nevertheless, the most com-mon living nature factors, environmental pH and tem-perature changes in particular, play leading role in engineering and study of “smart” polymer systems.  Polymer hydrogels with pH- and thermo-responsive functions are of primary importance in biomedical in-vestigations connected with the development of phar-maceuticals characterized by prolonged action and tar-geted delivery for molecular separation (cut-off), con-trolling enzyme activity and development of materials for biocompatibility improvement [2-3]. Application of such hydrogels in physico-chemical processes associat-ed with pressure and other thermodynamic parameters changes is restricted by the gel structure instability. Transport through swollen hydrogels by means of con-vective flow becomes possible only when the gel is sta-bilized in nanoporous substrate and retains its integri-ty [4]. Therefore, combination of pH- and thermo-responsive hydrogel properties with structural and mechanical merits of polymer membranes opens unique ways for the development of stable “smart” polymer systems with numerous promising fields of application. The aim of the present work is to study combination of the functions of manufactured ultra-filtration mem-branes with pH- and thermo-responsive hydrogels, as well as study of working parameters of the obtained nanocomposite systems.  2. MATERIALS AND METHODS  Manufactured ultrafiltration polyvinylidenfluoride (PVF) (UV 150-T) membranes with cut-off 150 kDa of Microdyn Nadir production (Germany) were used for modification. Since PVF membranes are chemically stable, the modification was carried out by accomplished hydrogel formation in membrane pores using radical polymeri-zation. N-isopropylacrylamide (NiPAA) and allyla-minehydrochloride (AAm) were chosen for this process. N,N-methylenebisacrylamide (MBA)  as a cross-linking agent and  components of the redox initiating system of ammonium persulphate (PSA) and tetramethylenedi-amine (TMED) were used without prior purification. Components of gel-forming composition were ho-mogenized on the ultrasound bath for 2 min, cooled to 0oC followed by 2 min argon bubbling through the spec-ified composition. Then the composition was triply passed in vacuum through manufactured ultrafiltra-tion membranes and placed in gauge between two flat-paralled glass plates for 1 hour to accomplish polymeri-zation. Prepared composite membranes were multiply washed in excess of distilled water. Concentration of cross-linked polymer in hydrogel was 21% (mass), con-centration of a cross –linking agent constituted 0.13% (mass) and the ratio of NiПАА and AAм in the compo-sition was equal to 9:1 (mass). Equilibrium swelling ratio was found by the follow-ing formula: Q=(ms-md)/md, where ms and md is mass of an equally swollen and dried sample, respectively. Re-sults of 10 parallel measurements were averaged in the process of calculation. Study of the swelling degree of copolymer hydrogels was carried out at pH 1.69; 6.86; and 9.18 in the temperature range from 5 to 54oC. Membrane separation characteristics were studied by dead-end ultra-filtration stirred cell Amicon 8050 (Millipore, USA)  0.01% water solution bull insulin with molecular mass of 6.0 kDa were used in order to find retention coefficient (R%) of the prepared membranes.  3. RESULTS AND DISCUSSION   Sensitive properties of specific components of pH- and thermo-sensitive hydrogels are due to information-al restructuring of macromolecular chains resulted from changes in the ratios of hydrophilic – hydrophobic interactions both of polymer chains themselves and  V.V. KONOVALOVA, G.A. POBIGAY, YU.M. SAMCHENKO ET AL PROC. NAP 2, 02FNC15 (2013)   02FNC15-2 those of solvent molecules. Synthetic weak acidic or weak basic polyelectrolytes are widely used for this purpose, whose chain confor-mation depends on dissociation degree of ionogenic groups [5]. Poly-N-isopropylacrylamide (PiPAA) is one of the most wide-spread thermo-sensitive polymers. Slight temperature changes at about critical value (32oC for PiPAA) result in reverse phase transition due to folding and unfolding of polymer macromolecules. At tempera-tures higher than critical, part of hydrophobic interac-tions of chains increases and polymer solubility de-creases. If temperature is lower than critical polymer-solvent interactions are prevailing leading to polymer hydrophylization and its transition in a soluble form [6]. Hydrogel swelling coefficient is an important pa-rameter determining quantity of a solvent in hydro-gelequilibrium state and is the function of polymer network structure, cross-linking degree, hydrophily  and functional group dissociation degree, that, in turn, depends on temperature, ionic strength and media pH.  NiPAA-based homopolymers swelling coefficient is almost non-dependent on media pH. NiPAA copolymeri-zation with various monomers allows purposefully change swelling curves character and phase transition temperature (Tp) of polymer hydrogels. Thus, addition of hydrophilic chains results in Tp growth, while that of hydrophobic ones in its decrease [7]. As is seen from Fig.1, phase transition temperature for the polymer containing 10% of allylaminehydrochlo-ride constitutes 35-37oC, a little bit higher value than that for PiPAA homopolymer. Allylamine is a monomer containing hydrophilic amino-groups, therefore its in-troduction into the synthesized mixture in the quantity of 10% (mass) causes rise in phase transition tempera-ture. Nevertheless, as it can see from differential swell-ing curves, pH influence on the speed of the system response to temperature changes is considerable, thus it can be stated that hydrogel structure depends both on temperature and pH of the environment.  00,511,522,520 30 40 50 60dQ/dTТ, 0СpH=1,68pH=6,86  Fig. 1 – Differential temperature dependence of hydrogel swelling degree based on NiPAAm (9:1);  Among membrane main transport characteristics are their productivity and selectivity. As is known from Gagen-Pausel equation, voluminous flow through membrane is inversely proportional to solution viscosi-ty, hence with the rise of temperature the membrane productivity grows linearly, while its selectivity re-mains almost unchanged. Separation (cut-off) and transportation characteristics of the obtained PVF-PiPAA-AAm membranes are given in Fig.2 and Fig 3. Obtained membranes also demonstrate thermo- and pH-sensitivity, but pH- and temperature dependences of voluminous flow values and retention coefficient dif-fer substantially. Changes of differential and integral curves of the voluminous flow at various pH (Fig.2) show that the membranes demonstrate phase transi-tion at 35oC. Here pH influences both speed of the sys-tem response on temperature change and temperature interval itself. In acidic and neutral pH, differential curves peaks are at 35o C and 37o C, respectively. The prepared membranes show the quickest re-sponse to temperature changes in acidic medium, while the slowest response is observed in neutral one due to the decrease of swelling degree of amino-containing hydrogels at pH increase. Fig.2 shows that at temperature lower than that of phase transition, voluminous flow does not practically depend on temperature in neutral and acidic pH con-tradicting Gagen-Pausel equation. The above-mentioned fact means that in this case membrane transport properties are determined by hydrogel struc-ture and are not influenced by the morphology of PVF membrane. Classical increase of the voluminous flow value with the temperature growth is observed at pH 9.5 when hydrogel has the lowest swelling degree.      Fig. 2 – Integral (1) and differential (2) dependences on water flux (Jv) of PVF-nanocomposite membrane versus tempera-ture and pH   NANOCOMPOSITE MEMBRANES WITH PH- AND THERMO-SENSITIVE FUNCTION PROC. NAP 2, 02FNC15 (2013)   02FNC15-3 The obtained membranes are characterized by high retention coefficient that is pH- and temperature func-tion, as well (fig3).  606570758085909515 25 35 45T, 0CR,%pH=5,5pH=3,2 pH=9,5  Fig. 3 – Retention coefficient of insulin for PVF-nanocomposite membrane versus temperature and pH.  The highest retention coefficient is characteristic for the membrane at acidic pH due to ionization of hydro-gel amino groups. When pH value changes from 3.0 to 9.5, retention coefficient decreases by 25-40% depend-ing on temperature. It is worth mentioning that insulin retention coefficient increases with the increase of temperature and growth of voluminous flow at temper-atures higher than that of phase transition. At neutral pH, retention coefficient increase at the expense of phase transition is from 70 to 87%, while for acidic pH this value constitutes from 80 to 95%. This can be ex-plained by the  peculiarities of the formation of compo-site hydrogel polymer membranes with different sur-face nature initiating mixture of monomers does not get in the membrane porous space and hydrogel is formed on its surface in the process of hydrogel for-mation on hydrophobic polyvyniliden fluoride mem-branes. Hydrogel membrane formed in this case is a prototype of dynamic membrane, with its own struc-ture and does not depend on porous structure of carrier membrane. Thus, hydrogel structure is thickened due to phase transition resulting on retention coefficient increase.  4. CONCLUSIONS  Nanocomposite membranes were formed with the help of hydrogel immobilization in polyvinylidenfluo-ride manufactured ultra-filtration membranes  PiPAA and AAm (9:1)-based hydrogels have been synthesized using radically initiated copolymerization. Hydrogel temperature dependence of hydrogel swelling degree in pH range of 1.68 to 9.18 was studied, and  temperature of phase transitions found to be equal to 35-370C. The membrane transport characteristic has been investigated. It was found that at neutral and acidic pH up to Tp, transport properties of modified mem-brane are determined by hydrogel structure and do not depend on membrane morphology. Membrane produc-tivity and retention coefficient increase by 15-20% pre-sumably due to thickening of hydrogel membrane po-rous structure.   REFERENCES  1.   W. Feng, S.H. Patel, M.-Y. Young et al., Advan. in Poly-mer Tech.. 26, 1(2007). 2. Aguilar M.R., C. Elvira, A. Gallardo, B. Vázquez, J.S., Topics in Tissue Engineering. 3, 1 (2007). 3. J. J. Kim, K. Park, Bioseparation. 7, 177 (1999). 4. Q. Yang, N. Adrus, F. Tomicki, M. Ulbricht, Journal of Materials Chemistry. 21, 2783 (2010). 5. S. Minko , J. of Macromol. Sci. Part C: Polymer Rev., 46, 397 (2006). 6. E.C. Cho, J. Lee, K. Cho, Macromolecules. 36, 9929 (2003). 7. W.F. Lee, Y.-H. Lin, J. of Mater. Sci., 41, 7333 (2006).  

Nanocomposite Membranes with pH- and Thermo-sensitive Function

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