ATOMIC FORCE MICROSCOPY AND STRUCTURAL INVESTIGATIONS OF R-BAPB-TYPE POLYIMIDE FILMS MODIFIED BY CARBON NANOFIBERS

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1 УДК ATM FRE MRSPY AND STRUTURAL NVESTGATNS F R-BAPB-TYPE PLYMDE FLMS MDFED BY ARBN NANFBERS G.N. Gubanva 1, T.E. Sukhanva 1, M.E. Vylegzhanina 1, A.. Grigriev 1, V.A. Bershtein 2 1 nstitute f Macrmlecular mpunds f the Russian Academy f Sciences, , Blshy pr., 31, St.-Petersburg, Russia, fax; +7 (812) , gubanva@imc.macr.ru 2 ffe Physic-Technical nstitute f the Russian Academy f Sciences, St.-Petersburg, Russia n ur previus wrks [15], the crystallizatin behavir f a new semicrystalline plyimide (P) based n 1,3 bis (3,3',4,4'-dicarbxyphenxy)benzene (R) and 4,4'-bis-(4- aminphenxy)biphenyl (BAPB) with the chemical structure: N N n was investigated. t was fund that variatin f prcessing cnditins, additin f lw mlecular weight bisimides, varying f the mlecular weight f the P, and additin f carbn fibres [4] r carbn nantubes [5] significantly influenced crystalline mrphlgy f this plymer and its ability t crystallize frm melt. n this paper, we reprt, as a next step in these investigatins, an influence f uniaxial drawing and carbn nanfiber mdificatin f these P films n their supermlecular structure and crystallinity Experimental The R-BAPB P films f μm thickness were prepared as fllws: ply(amic acid) (PAA) was btained by plycndensatin f 1,3-bis(3,3`,4,4`-dicarbxyphenxy)benzene (R) and 4,4`-bis-(4-aminphenxy)biphenyl (BAPB) in a 25 wt. % slutin f N-methyl-2- pyrrlidne (NMP) at 25 and subsequent drying at 80 fr 20 h. P films were prepared frm the PAA by casting n sda lime glass plates and ven curing under air. midizatin was achieved by heating the films in air ven fr 15 min at 50 and 100, then rapid heating till 280 and slw heating during 2 h till 300. A dilute Vapr Grwn arbn Fibers (VGF) suspensin in NMP (0.1 vl. %) was prepared by hmgenizatin fr 10 min in ultrasnic bath (40 khz). The BAPB diamine was added int the VGF suspensin. The VGF and diamine mixture was stirred fr 20 min befre adding dianhydride and phtalic anhydride (PA) μm thick VGF/P cmpsite films were prepared with 15 vl.% frm VGF- PAA slutin as fr the neat P films. Uniaxial drawing was perfrmed using labratry set-up [4] at 250 up t draw rati λ = 5.5. P film samples filled with 3 wt. % VGF) were prepared accrding t the prcedure described in [3]. Atmic frce micrscpy (AFM), wide angle X-ray scattering (WAXS) and differential scanning calrimetry (DS) techniques were used fr the structural characteriza- 38

2 tin f films. Results and discussins DS curves btained fr P and nancmpsite samples under study display three distinctive features: the glass transitin with T g in the regin f С; extherm in the regin f abut , and melting endthermic peaks with the maxima at T m = T g as well as the narrw glass transitin range ΔT g = 8±2 С are rather stable fr these films and practically d nt change at the secnd scan. This allwed t suppse that amrphus phase in this type f P remains quasi-independent, at the first apprximain, frm the crystalline phase. Therefre, R-BAPB P may likely be cnsidered as tw-phase system, unlike mre cmplicated dynamic/structural behavir f typical semi-crystalline plymers. An extherm may be assciated with nt nly crystallizatin f P films but als with energy release as a cnsequence f imprvement f mlecular packing in amrphus phase. The value f melting endtherm depended n several factrs including the drawing temperature and mdificatin by NF. Sme f DS data are listed in Table 1. DS data shw that the intrductin f nanfibers increases the enthalpy f melting f P films mre effectively than uniaxial drawing. ntrarily, enthalpies f extherms after uniaxial drawing f R-BAPB and VGF/R-BAPB P films are ntably higher than fr undrawn samples. WAXS data als cnfirm that uniaxial drawing f P films at temperature higher than the glass transitin temperature (abve 215 ) increases the crystallinity degree up t 20 %, at draw rati λ > 4. Accrding t WAXS data, intrductin f carbn nanfibers (3 wt. %) leads t increasing the degree f crystallinity frm 5 t 10 % fr undrawn VGF/R-BAPB sample. DS data btained fr R-BAPB and VGF/ R-BAPB P films in the range f , at the heating rate f 10 /min Sample Scan T g, 1. Undrawn P film 2. Drawn P film, λ= Undrawn P film, with 3 % VGF 4. Drawn P film, with 3 % VGF, λ= GVF/P film drawn, at wt% GVF, (λ = 5.5) and annealed at 280 /3h Δ p, J/(g K) Extherm Temp. regin, ΔH ex, J/g T m, Endtherm Table 1 ΔH m, J/g

3 МЕТОДОЛОГИЧЕСКИЕ АСПЕКТЫ СКАНИРУЮЩЕЙ ЗОНДОВОЙ МИКРОСКОПИИ 2008 Simultaneusly, the entalpy f melting attains 13 J/g (Table 1). Uniaxial drawing f VGF/R-BAPB P films and subsequent annealing at 270 led t grwth f the degree f crystallinity up t 45 % (WAXS data) and 57 % (DS data). Mrever, the latter drawn nancmpsite films became after heating up t 300 almst ttally crystalline. t shuld be als nted that the crystallites rientatin in P films has nt been detected by WAXS after drawing as we usually bserved fr the ther semi-crystalline Ps [6]. DS curves f VGF/R-BAPB P films display, after their uniaxial drawing at 250, tw endtherms, at T m1 = 313 and T m2 = 329, which may crrespnd t melting f tw different types f crystallites (Fig. 1, b), while undrwn P films is characterized by the nly ne endthrms at 322 (Fig. 1, a). p = 0.1 J/(g K) p = 0.1 J/(g K) a) b) Fig. 1. DS thermgrams f : а) R-BAPB at 10 /min scan rate fr P film, after amrphisatin at 360 /10 min and then crystallized at 280 /2h; b) DS thermgrams f VGNF/ R-BAPB (1 wt.% f VGNF) at 10 /min scan rate fr P film drawn at 250 (λ = 5.5). first scan, secnd scan This bservatin is in accrdance with AFM data which display tw drastically different types f mrphlgy in the drawn R-BAPB P films filled with 3 wt. % VGF (Fig. 2, a). While the first type has a spherulitic mrphlgy, the secnd type resembles the shish-kebab structure. t is highly prbable that this peculiar mrphlgy is cnnected with shear stresses during preparatin f these filled P films. Under higher reslutin (Fig. 2, b), stack f lamellae with a thickness frm 60 t 180 nm and tw kink bands crssing the film surface (at the angle abut 30 t ne anther) are clearly seen. nsequent annealing at 280 during 3h leads t appearance f third type f mrphlgy quasi-lammelar (Fig. 2, c, d), which fllwed by essencial increasing f melting enthalpy up t 43 J/g (table 1, sample 5). 40

4 a) b) nclusins c) d) Fig. 2. AFM images f VGF/R-BAPB P film surface with 3 wt. % nanfibers, λ = 5.5 (a, b); annealed film at 280 /3h (c, d) 1. nfluence f uniaxial drawing and embedded nanfiber mdificatin f the P films n their supramlecular structure was shwn by AFM, DS and WAXS. 2. The presence f tw different crystalline mrphlgies was detected by AFM methd. Als, tw melting endtherms bserved by DS after drawing f VGF/P nancmpsite films cnfirmed AFM data. 3. Drawing f the VGF/P nancmpsite film and subsequent annealing result in failure f the initial spherulitic mrphlgy and frmatin f the quasi-fibrillar type f mrphlgy. References 1. Yudin V.E., Svetlichnyi V.M., Gubanva G.N., Didenk A.., Sukhanva T.E., Kudryavtsev V.V. // J. Appl. Plym. Sci Sukhanva T.E., Grigriev A.., Svetlichnyi V.M., Yudin V.E., Gubanva G.N., Matveeva G.N., Vlkv A. Didenk A.L., Kudryavtsev V.V., Ratner S. and Marm G. Plyimides and ther High Temperature Plymers / Ed. by K.L. Mittal Vl. 4. Pp Суханова Т.Е., Вылегжанина М.Э., Новиков Д.В., Кутин А.А. и др. // ВM Т. 50, 3. С

5 МЕТОДОЛОГИЧЕСКИЕ АСПЕКТЫ СКАНИРУЮЩЕЙ ЗОНДОВОЙ МИКРОСКОПИИ Yudin V.E., Svetlichnyi V.M., Gubanva G.N., Didenk A.., Sukhanva T.E, Kudryavtsev V.V. Plyimides and ther High Temperature Plymers // K.L. Mittal, Ed; VSP, USA, 2003, Vl. 2, Yudin V.E., Svetlichnyi V.M., Shumakv A.N., Letenk D.G. // Macrml. Rapid. mmun Smirnva V.E., Gfman.V., Gubanva G.N., Yudin V.E., Sukhanva T.E. // Russ. J. Appl. hem