MECHANICAL AND PHYSICAL PROPERTIES OF AMORPHOUS SOLIDS BASED ON (CH3) 2SiO-SiO2 GELS

HAL Id: jpa-00222480

https://hal.archives-ouvertes.fr/jpa-00222480

Submitted on 1 Jan 1982

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

MECHANICAL AND PHYSICAL PROPERTIES OF AMORPHOUS SOLIDS BASED ON (CH3) 2SiO-SiO2

GELS

H. Schmidt, A. Kaiser, H. Patzelt, H. Scholze

To cite this version:

H. Schmidt, A. Kaiser, H. Patzelt, H. Scholze. MECHANICAL AND PHYSICAL PROPERTIES OF

AMORPHOUS SOLIDS BASED ON (CH3) 2SiO-SiO2 GELS. Journal de Physique Colloques, 1982,

43 (C9), pp.C9-275-C9-278. �10.1051/jphyscol:1982951�. �jpa-00222480�

Colloque C9, supplement au n°12, Tome 43, decembre 1982 -page C9-275

MECHANICAL AND PHYSICAL PROPERTIES OF AMORPHOUS SOLIDS BASED ON ( c H 3 ) 2 S i O - S ± 0

GELS

H. Schmidt, A. K a i s e r , H. P a t z e l t and H. S c h o l z e

Fvaunhofer-Institut filr Siliaatforsehung, D-8700 Wilrsburg, F.R.G.

Résumé. - L'influence des conditions des réactions et des compositions sur les pro- priétés physiques des gels dans le système (CH,)2SiO-Si02 étaient étudiés. Ces maté- riaux sont préparés par une cohydrolyse et une cocondensation des composés SifOEt)^

et (CHg)2Si(0Et)2. Ils étaient développés comme abrasifs à la durée d'application limitée et ils sont utilisés pour leurs effets cosmétiques et médicales, par exemple, pour amollir la peau humaine. Les réactions d'hydrolyse et de la condensation sont examinées par des méthodes infrarouges et par la spectromêtrie de masse. Les maté- riaux étaient caractérisés par les techniques SEM, SAXS et BET. Pour définir les propriétés abrasifs on a développé une méthode spéciale.

Abstract. - The influences of reaction conditions and compositions on the physical properties of gels in the system (.CH3)2SiO-SiC>2 were investigated. These materials are prepared by eohydrolysis and cocondensation of (CH3)2Si(0Et)k and were developed for being used as abrasive'powders with limited effectiveness. They are applied for cosmetical or medical purposes, e.g. smoothening the human skin. Hydrolysis and con- densation are monitored by IR, NIR and MS methods, for characterization of the materials SEM, SAXS, BET surface measurementsj and a special abrasive test were used.

1. Introduction

Abrasives are widely used in technique and industry. In general abrasive powders have to be very hard in order to keep up their abrasion properties as long as possi- ble. For special applications like cosmetic treatment or therapies of the human skin it is necessary to use softer abrasives or abrasives with limited effectiveness in order to avoid hurt. Moreover, these materials have to be absolutely free from toxic or irritating components.

For the latter reason, silica or silicones are very suitable, but silicones as abrasives are too soft, while silicas for skin therapy in general are too hard'. The development of mixed polymers based on [SiOlJ^

and [(CE^^SiOg]

should lead to materials, however, with suitable properties. Therefore, it seems to be necessary to know the basic influences of reaction conditions and compositions on the material properties. The reaction rates of hydrolysis, especially in mixed systems are of special interest, since reactive monomers are produced and the following cross-link- ing reaction will be strongly influenced by the concentration of these reactive mono- mers. The hydrolysis and condensation reaction will be affected by the type of cata- lyst, solvent, concentration of starting components and temperature.

2. Experimental

The materials were prepared by hydrolysis and condensation of Si(0Et)4 and (CH3)2Si(0Et)2 in ethanolic solution at room temperature in beakers or in a closed system under reflux conditions [1 ,2~\ . Aqueous solutions of HC1 and ammonia were used as catalysts. The hydrolysis and condensation reactions were investigated by IR spec- troscopy monitoring the HgO deformation band at 165O cm

[3,

*]. Measuring the bands at 5155 (H

0) and 1*820 cm~1 (EtOH) in the NIR region it was possible to separate the hydrolysis from the condensation reaction. The viscosity of the reacting system was measured by use of an Ubbelohde viscosimeter. MS investigations were carried out

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982951

C9-276 JOURNAL DE PHYSIQUE

u s i n g a GC-MS system. For c h a r a c t e r i z i n g t h e a b r a s i o n behaviour of t h e m a t e r i a l s t h f r a c t i o n between 0.3 and 0.4 mm was grinded between rubber p l a t e s under p r e s s u r e s i m u l a t i n g t h e a b r a s i v e procedure on t h e human s k i n and t h e amount of t h e uncrushed p a r t i c l e s was determined. The s p e c i f i c s u r f a c e a r e a was measured by t h e BET method, m i c r o s t r u c t u r e was c h a r a c t e r i z e d by SEM and SAXS. The p o r o s i t y was determined by an a l c o h o l p e n e t r a t i o n method.

3. R e s u l t s and d i s c u s s i o n

I n o r d e r t o determine t h e i n f l u e n c e of c a t a l y s t t y p e and composition on t h e mata r i a l p r o p e r t i e s , d i f f e r e n t s e r i e s of m a t e r i a l s were p r e p a r e d . Solvent t y p e and com- pound c o n c e n t r a t i o n and temperature (room t e m p e r a t u r e ) were kept c o n s t a n t . To cha- r a c t e r i z e t h e p r o d u c t s , l o o s e weight, p o r o s i t y , BET s u r f a c e , and t h e a b r a s i o n be- haviour were determined. Table 1 g i v e s a survey over t h e r e s u l t s obtained.

Table 1 . Composition and p r o p e r t i e s of mixed condensates

C a t a l y s t composition l o o s e weight BET p o r o s i t y a b r a s i o n t e d

SiO : ( C H 3 ) 2 ~ i ~ s u r f a c e uncrushed

f'mol-% ) ( g/cm3) (m2/g) ( I I & / ~ ) fr a c t i o n (wt

Basic d i f f e r e n c e s i n t h e m a t e r i a l p r o p e r t i e s a r e obvious. The s p e c i f i c s u r f a c e a r e a r e remarkably lower with t h e products prepared with ammonia a s c a t a l y s t . The H C 1 c a t a l y z e d m a t e r i a l s a r e compact, c l e a r and homogeneous l o o k i n g , t h e N H 3 c a t a l y z e d ones a r e cloudy and d i s a g g r e g a t e d . S i m i l a r r e s u l t s a r e r e p o r t e d by Brinker [5] on pure s i l i c a s . By SEEM t h e t y p i c a l d i f f e r e n c e s i n t h e m i c r o s t r u c t u r e become v i s i b l e

( f i g . 1 ) .

F i g . 1 : Scanning e l e c t r o n micrographs o f Si02/(CH )$3iO g e l s (molar r a t i o n = 7 0 / 3 1

prepared with 1 N H C 1 ( l e f t ) and 3 N NH3 f r i g h t ) a s c a t a l y s t s .

t h e range of 10 t o 100 nm d e s p i t e of remarkable p o r o s i t i e s and high BET s u r f a c e a r e a s . This might be due t o t h e microporosity with p o r e diameters below 5 nm, a s in- d i c a t e d by e v a l u a t i o n of BET isotherms. I n t h e c a s e of ammonia c a t a l y s i s SAXS measurements show s t r o n g inhomogeneities. These inhomogeneities a r e observed with t h e r a t h e r d i s a g g r e g a t e d m a t e r i a l s shown i n f i g . 1 a s w e l l a s with c l e a r and compact m a t e r i a l s which can be p r e p a r e d with low NH3 c o n c e n t r a t i o n s . The l a t t e r m a t e r i a l s a l s o show h i g h s p e c i f i c s u r f a c e a r e a s and a c l e a r and homogeneous appearance. So t h e SAXS p l o t s have t o be i n t e r p r e t e d a s s t r u c t u r a l inhomogeneities.

As a consequence, t h e d i f f e r e n c e s i n m i c r o s t r u c t u r e a f f e c t s t r o n g l y t h e mechani- c a l p r o p e r t i e s a s i n d i c a t e d i n t a b l e 1. How can t h e s e d a t a be understood? As mention- ed above, t h e p r o c e s s of h y d r o l y s i s and condensation should i n f l u e n c e t h e c r o s s - l i n k i n g r e a c t i o n and t h e mechanical and p h y s i c a l p r o p e r t i e s . With Hf c a t a l y s i s t h e r a t e of h y d r o l y s i s of S i ( O E t ) 4 i s about 2-3'103 t i m e s slower t h a n t h a t o f

( C H ~ ) ~ S ~ ( O E ~ ) ~ with a l i n e a r dependence of r a t e on H+ c o n c e n t r a t i o n . The d a t a could be confirmed by GC-MS i n v e s t i g a t i o n and by v i s c o s i t y measurements of r e a c t i n g sy- stems of t h e s i n g l e components. NH3 k i n e t i c s a r e completely d i f f e r e n t , t h e hydro- l y s i s r a t e of ( C H 3 ) 2 ~ i ( ~ ~ t ) 2 i s slower t h a n t h a t of s i ( O E t ) & and d e c r e a s e s with i n - c r e a s i n g NH3 c o n c e n t r a t i o n . Fig.2 shows s c h e m a t i c a l l y t h e c h r o n o l o g i c a l o r d e r of t h e d i f f e r e n t s i n g l e r e a c t i o n s t e p s with H C 1 and NH3 c a t a l y s i s .

F i g . 2: Scheme of t h e c h r o a o l o g i c a l o r d e r o f t h e s i n g l e r e a c t i o n s t e p s of g e l forma- t i o n with H C 1 and NH3 c a t a l y s i s . The o r d i n a t e expansion of t h e b a r s r e f e r s t o t h e r e a c t i o n r a t e .

1 : Hydrolysis of ( C H 3 ) 2 S i ( ~ ~ t ) 2 2: Hydrolysis of S i ( O E t ) &

3: Condensation of ( C H 3 ) 2 S i ( ~ ~ ) 2 4 : Condensation of Si(OH)I,

I n t h e H C 1 c a t a l y z e d c a s e a low r a t i c o f condensation t o h y d r o l y s i s r a t e r e - s u l t s . S i n c e condensation o c c u r s slowly and high c o n c e n t r a t i o n s of r e a c t i v e com- pounds of both t y p e s a r e a v a i l a b l e , a f a i r l y homogeneous network may be b u i l t up.

I n t h e NH3 c a t a l y z e d c a s e , h y d r o l y s i s of ( C H 3 ) p S i ( O ~ t ) 2 t a k e s p l a c e very slowly s o t h a t a t f i r s t t h e condensation of S ~ ( O H ) ~ by forming Si02-rich primary p a r t i c l e s may occur. L a t e r on (CH3)2Si0 w i l l be i n c o r p o r a t e d i n i n c r e a s i n g amounts. It i s n o t q u i t e c l e a r up t o now how f a r p o s s i b l e inhornogeneities r e s u l t i n g from t h e s e k i n e t i c r e a s o n s may be r e l a t e d t o t h e SAXS d a t a . So f a r , more d a t a have t o be o b t a i n e d .

Concerning t h e a b r a s i o n , only a weak i n f l u e n c e of t h e composition could be ob- served ( s e e t a b l e 1 ) . While t h e compositions 100/0 and 90/10 a r e t o o h a r d , t h e com- p o s i t i o n 50/50 was t o o e l a s t i c due t o t h e high amount o f l i n e a r polymerizing

( C H ~ ) ~ S ~ ( O E ~ ) ~ . Since a r e t a i n i n g of 60-80% of uncrushed p a r t i c l e s a f t e r having p e r -

formed t h e a b r a s i o n t e s t was found t o be most s u i t a b l e f o r p r a c t i c a l purposes,

f u r t h e r o p t i m i z a t i o n was based on 70/30 composition. By v a r i a t i o n o f t h e c a t a l y s t

C9-278 JOURNAL DE PHYSIQUE

c o n c e n t r a t i o n t h e a b r a s i o n could be v a r i e d i n a wide range a s shown i n t a b l e 2 . Table 2. Abrasion behaviour of 70130 condensates prepared with v a r i o u s c a t a l y s t

c o n c e n t r a t i o n s

H C ~ c o n c e n t r a t i o n ( N ) 0.01 0.1 1 6 12

Uncrushed f r a c t i o n (Tit.%) Loose weight

(g/cm3)

C a t a l y s t c o n c e n t r a t i o n s between 6 and 12 N H C 1 l e a d t o s u i t a b l e p r o d u c t s . The l o o s e weight r e f l e c t i n g t h e d i s a g g r e g a t i o n s t a t e o f t h e m i c r o s t r u c t u r e checks w e l l w i t h t h e a b r a s i o n .

On t h e b a s i s of t h e s e r e s u l t s a l a r g e s c a l e p r e p a r a t i o n t e c h n i q u e was developed.

S i n c e f o r t e c h n i c a l purposes t h e r e a c t i o n a t room temperature r e q u i r e s t o o l o n g t i m e , t h e p r o c e s s was c a r r i e d o u t under r e f l u x c o n d i t i o n s . S u i t a b l e p r o d u c t s could b e achieved by optimizing t h e c a t a l y s t c o n c e n t r a t i o n . By t h i s , it was p o s s i b l e t o p r e p a r e taylormade a b r a s i v e s f o r very s p e c i a l purposes.

4. References

[ I ] No11 ,W. : Chemie und Technologic d e r S i l i c o n e . 2 .Aufl . Weinheim: Verlag Chemie I 968

[2-1 Iler,R.K.: The chemistry of s i l i c a . New York: Wiley 1979

13 1 Shaulov,Yu.Kh. , Shtrambrand,Yu.M., Zhukova,L.A., and Ryabenko,E.A., Z . F i z .

mim. 9 ( 1 9 7 5 ) , 1590

[b] Schmidt ,H. and Kaiser,A., Glastechn.Ber. 54 ⁽¹⁹⁸¹ ) 110 1 ³³⁸

[5] Brinker,C. J. , Keefer,K .D., Schaefer,D .W., and Ashley ,C .S. , J .Non-Crystalline

S o l i d s 48 ^{( 1982), 47}