A new simple reaction-diffusion system is presented focusing on pattern formation phenomena as consecutive precipitation fronts and distortion of the precipitation front.The chemical system investigated here is based on the amphoteric property of aluminum hydroxide and exhibits two unique phenomena. Both the existence of consecutive precipitation fronts and distortion are reported for the first time. The precipitation patterns could be controlled by the pH field, and the distortion of the precipitation front can be practical for microtechnological applications of reaction-diffusion systems

Izsák, F.

Lagzi, I.

Ripszam, M.

Volford, A.

English

Izsak, F.

University of Twente Research Information

Systematic Front Distortion and Presence of Consecutive Fronts in a Precipitation SystemAndrás Volford,† Ferenc Izsák,‡,§ Mátyás Ripszám,| and István Lagzi* ,|Department of Chemical Physics, Budapest UniVersity of Technology and Economics,Budapest H-1521, Hungary, Department of Applied Analysis, Institute of Mathematics, Eo¨tVös UniVersity,P.O. Box 120, Budapest H-1518, Hungary, Department of Applied Mathematics, UniVersity of Twente,P.O. Box 217, Enschede 750 AE, The Netherlands, and Department of Physical Chemistry, Institute ofChemistry, Eo¨tVös UniVersity, P.O. Box 32, Budapest H-1518, HungaryReceiVed: January 20, 2006; In Final Form: February 13, 2006A new simple reaction-diffusion system is presented focusing on pattern formation phenomena as consecutiveprecipitation fronts and distortion of the precipitation front. The chemical system investigated here is basedon the amphoteric property of aluminum hydroxide and exhibits two unique phenomena. Both the existenceof consecutive precipitation fronts and distortion are reported for the first time. The precipitation patternscould be controlled by the pH field, and the distortion of the precipitation front can be practical formicrotechnological applications of reaction-diffusion systems.Technological application of precipitation reaction-diffusionsystems has a great and highly increasing relevance.1-3 Pre-cipitation patterns (PP) can emerge, where the diffusion of two,usually inorganic, species are coupled with their reaction.4-6The existence of such patterns is usually explained by theinstability of colloidal substances arising from the reactants.6,7The classical precipitation (Liesegang) patterns are static andstationary in the sense that the formed precipitation objects(bands, rings, or more complex patterns) stay at the given formedposition. Instead of static patterns, dynamically changingprecipitation patterns can be formed, if the complex formationof precipitate is possible; for example, in a classical Liesegangexperimental setup a precipitation front moves through thereaction domain.8-11Recently, focusing to micro- and nanotechnological applica-tions of reaction-diffusion systems a detailed study on small-scale phenomena provides an alternative way of designingmicrostructures (diffraction gratings, planar Fresnel-like lenses)1and control pattern formation in small scales.12-14 An advancedapplication of such a structure is the fabrication of surfaces withnanoscopic waves of linearly increasing heights.15There are several systems in which a moving precipitationfront has been observed (Hg2+/I-, Co2+/NH4OH, Cr3+/OH-;inner/outer electrolyte). In a usual setup, the inner electrolyte(represented by cations) is distributed homogeneously in a gel(e.g., gelatine, agar-agar, agarose, PVA), while the outerelectrolyte diffuses into this medium from outside. Sedimenta-tion and hydrodynamic instability are thus ignored. Precipitateformation (HgI2, Co(OH)2, Cr(OH)3) is preferred at the junctionpoint of the electrolytes; at the same time, the excess of theouter electrolyte behind the front reacts with precipitate bycomplex formation ([HgI4]2-, [Co(NH3)6]2+, [Cr(OH)4]-) pro-ducing a soluble complex (redissolution). In such a way onesingle precipitation pulse can be detected,11-13 which evolvesin the gel driven by diffusion with a decreasing velocity.We have constructed a new system (Al3+/OH-), which canproduce several well-separated fronts varying periodically thepH of the central reservoir because of the amphoteric propertyof aluminum hydroxide. An agarose gel containing AlCl3 (innerelectrolyte) of a given concentration was prepared as follows.Agarose (Reanal) was dissolved in distilled water in such a waythat it produced a solution 1 V/m %, which was heated to 70-80 °C and stirred until the solution became crystal clear. Thesolution was then mixed with the given amount of AlCl3*6H2O(Reanal) to prepare the inner electrolyte with a concentrationof 0.040 M in a Petri dish, which was held firmly horizontallyto obtain a uniformly thick gel. After the completion of thegelation process (1 h) the outer electrolyte (NaOH, 2.50 M)was placed into a hole (reservoir, cut out from the gel). Thepattern formation was monitored in transmitted light perpen-dicular to the gel surface by a digital camera (EOS-20D).Precipitation process and complex formation produced a well-visible and sharp thin aluminum hydroxide front by thefollowing reactionsThe front moved from the central reservoir by diffusive kineticsas the width of the pulse increased (Figure 1a). After the frontleft, the base in the reservoir was replaced by acid (HCl, 3.020M) and precipitate appeared at the interface due to the reversiblestep (eq 2). Excess of H+ redissolved the formed precipitate(eq 1) and a second, thin precipitation front evolved following* Corresponding author. E-mail: lagzi@vuk.chem.elte.hu.† Budapest University of Technology and Economics.‡ Department of Applied Analysis, Institute of Mathematics, Eo¨tvösUniversity.§ University of Twente.| Department of Physical Chemistry, Institute of Chemistry, Eo¨tvösUniversity.Al 3+(aq)+ 3H2O T Al(OH)3(s) + 3H+(aq) (1)Al(OH)3(s) + H2O T [Al(OH)4]-(aq)+ H+(aq) (2)45352006,110,4535-4537Published on Web 02/23/200610.1021/jp0604286 CCC: $33.50 © 2006 American Chemical Societythe first, wider one (Figure 1b). A third front can still beproduced by replacing acid with a base (NaOH) (Figure 1c).Further fronts cannot be produced because the free aluminumand its hydroxo complex diffuse from the gel to the reservoir.The periodic change of pH in the central reservoir produces aFigure 1. Evolution of aluminum hydroxide precipitation fronts varyingthe pH in the central reservoir. (a) The single precipitation front after2 h. (b) Two consecutive fronts after 2.5 h. (c) Three precipitation frontsafter 2.8 h. Initial conditions: [Al3+] ) 0.040 M; [NaOH]) 2.50 M(750µL); agarose gel thickness: 3.2 mm; central hole radius: 10 mm.After 2 h NaOH was replaced by acid ([HCl]) 3.020 M; 750µL).Half an hour later the reservoir was filled again with a base. The scalebar represents 1 cm.Figure 2. Systematic distortion of the precipitation fronts after 5 h:using (a) three, (b) four, (c) five, and (d) six peripheral reservoirs. Initialconditions: (1) agarose gel: [Al3+] ) 0.040 M, thickness: 3.2 mm;(2) radius of the central hole: 10 mm, [NaOH]) 2.50 M (750µL);(3) radii of the peripheral holes 9.0 mm, [HCl]) 3.020 M (505µL).The distance of the peripheral reservoirs from the central one is 3.4cm. The scale bar represents 1 cm.4536 J. Phys. Chem. B, Vol. 110, No. 10, 2006 Lettersnew pattern formation phenomenon compared to previoussystems using the amphoteric property of the precipitate.In micro- and nanotechnological applications of the reaction-diffusion systems (WETS: wet stamping technique),13 patternformation is determined by the geometrical restriction of thestamp (e.g., the pattern inherits the shape of the stamp). Beyondsuch geometrical constraints, it can be important to distort thepattern structure. In macroscales, the symmetric or asymmetricdistortion of PP by electric field has been done already;16-18 atthe same time, in microscales despite of some promisingexperimental investigations19 the theoretical background alongwith the numerical simulations have not yet been completed.Aluminum hydroxide exists only in a range of pH; anyway,either soluble complex or free Al3+ is present. Applying thisfact, various geometries of pattern can be produced, if the centralreservoir filled with NaOH is surrounded by some otherreservoirs containing HCl with a given setup: radius ofreservoir, distance from the central one, and concentration ofacid.At the first stage, as described above, a radially symmetricfront propagated from the boundary of the central reservoir. Thisevolution is driven mainly by the diffusion of OH- from thecentral one. Pattern formation did not occur around theperipheral holes because H+ does not produce precipitate withAl3+ (inner electrolyte); however, it may react with theprecipitate Al(OH)3 (eq 1). Relatively far from the centralreservoir, the pH field, determining the position and width ofthe front, is affected by H+ diffused from the peripheral holes(Figure 2). After some time the pH field becomes stationarybecause of the continuous fluxes of H+ and OH- and neutral-ization reaction between them. Consequently, PP will bestationary as well. Variation of the pH field ensures a systematiccontrol and distortion of a primarily radially symmetric pre-cipitation front even in microscales.In conclusion, we designed a new precipitation system inwhich unique phenomena have been observed because of theamphoteric property of the precipitate employed.Acknowledgment. We acknowledge the support of thePostdoctoral Fellowship (OTKA D048673) and OTKA grant(T-42708) of the Hungarian Research Foundation.Supporting Information Available: The movie shows theevolution of aluminum hydroxide precipitation fronts using threeperipheral reservoirs setup. It contains six frames (one frameper hour). Initial conditions: (1) agarose gel: [Al3+] ) 0.040M, thickness: 3.2 mm; (2) radius of the central hole: 10 mm,[NaOH] ) 2.50 M (750µL); (3) radii of the peripheral holes:9.0 mm, [HCl] ) 3.020 M (505 µL). The distance of theperipheral reservoirs from the central one is 3.4 cm. Thismaterial is available free of charge via the Internet at http://pubs.acs.org.References and Notes(1) Grzybowski, B. A.; Bishop, K. J. M.; Campbell, C. J.; Fiałkowski,M.; Smoukov, S. K.Soft Matter2005, 1, 114.(2) Bhattacharya, M.; Vlachos, D. G.; Tsapatsis, M.Appl. Phys. Lett.2003, 82, 3357.(3) Lebedeva, M. I.; Vlachos, D. G.; Tsapatsis, M.Ind. Eng. Chem.Res.2004, 43, 3073.(4) Liesegang, R. E.Naturwiss. Wochenschr.1896, 11, 353.(5) Hantz, P.J. Phys. Chem. B2000, 104, 4266.(6) Müller, S. C.; Ross, J.J. Phys. Chem. A2003, 107, 7997.(7) George, J.; Varghese, G.J. Colloid Interface Sci.2005, 282, 397.(8) Zrı́nyi, M.; Gálfi, L.; Smidróczki, EÄ .; Rácz, Z.; Horkay, F.J. Phys.Chem.1991, 95, 1618.(9) Sultan, R.; Sadek, S.J. Phys. Chem.1996, 100, 16912.(10) Das, I.; Pushkarna, A.; Agrawal, N. R.J. Phys. Chem.1989, 93,7269.(11) Lagzi, I.J. Phys. Chem. B2003, 107, 13750.(12) Bitner, A.; Fiałkowski, M.; Grzybowski, B. A.J. Phys. Chem. B2004, 108, 19904.(13) Klajn, R.; Fiałkowski, M.; Bensemann, I. T.; Bitner, A.; Campbell,C. J.; Bishop, K.; Smoukov, S.; Grzybowski, B. A.Nat. Mater.2004, 3,729.(14) Bensemann, I. T.; Fiałkowski, M.; Grzybowski, B. A.J Phys.Chem. B2005, 109, 2774.(15) Smoukov, S. K.; Bitner, A.; Campbell, C. J.; Kandere-Grzybowska,K.; Grzybowski, B. A.J. Am. Chem. Soc.2005, 127, 17803.(16) Shreif, Z.; Mandalian, L.; Abi-Haydar, A.; Sultan, R.Phys. Chem.Chem. Phys.2004, 6, 3461.(17) Bena, I.; Coppex, F.; Droz, M.; Ra´cz, Z. J. Chem. Phys.2005,122, 024512.(18) Bena, I.; Droz, M.; Ra´cz, Z. J. Chem. Phys.2005, 122, 204502.(19) Lagzi, I.Phys. Chem. Chem. Phys.2002, 4, 1268.Letters J. Phys. Chem. B, Vol. 110, No. 10, 20064537

Systematic front distortion and presence of consecutive fronts in a precipitation system

NARCIS 

Colloid Interface Sci.

Soft Matter

Systematic front distortion and presence of consecutive fronts in a precipitation system

Abstract

Similar works

Full text

Available Versions

University of Twente Research Information

NARCIS