272 JOURNAL OF COSMETIC SCIENCE 0.03 ----------.,.......--....---------------------.. 0.025 0.02 'iii )I( Ill a. i 0.015 .§ 0.01 0.005 a) 15°C - - - - - - -;- - - - - - - I - - ' ' • 1 - - - - - - - - - ---- - - - - - ... - - - - - -- - - I I I I --+--no vii. C ' '\. --2%vit.C • • • 10%vit.C c ______ 0 __ .'1!1!9� ______ C _______ , _______ , _ •• '- ' --e • 20%vit.C : .. • : -1: • 60%vit.C : ..._:..,. • - - - - - - � - - - - - - + - - - ' ' 0..--------------------------------...... )I( Ill a. 0 10 20 30 40 50 60 70 80 90 100 Water Content in Microemulsion (Wt%) 0.03 --------.---.,.......--....-----------.....-----.-----.-----, 0.025 0.02 I I I I I I - - - - - - I - - - - - - I - - - - - - T - - - - - - I - - - - - - 7 - - - - - - I - - - - - I ! I I ___ �1 ii�c- _ � _____ - l - _____ J _ - - - - _ J _ � -�- �- - - - - - ) _ - - - - - -:- - - - - - ) _ - - - - - - ,, --+--novlt. C .. i 0.015 --a -2% vit. C .. -& .. 10%vit.C --e • 20%vlt. C WI_� i - - - - - - " - - - - - _, - - - - - � _ - - - ' ! ' "\. .8 0.01 0.005 0..---------------------------------.. 0 10 20 30 40 50 60 70 80 90 100 Water Content in Microemulsion (Wt%) Figure 4. Influence of ascorbic acid concentration on the viscosity of the microemulsion region of the SDS/penranol/water system: (a) temperature l 5 ° C, (b) temperature 22°C, (c) temperature 30°C, and (d) temperature 40°C. The microemulsion was prepared by titration of penranol and sodium dodecyl sulphate mixtures of various weight ratios by ascorbic acid water solution. This mixture was vigorously mixed to obtain a clear and highly stable microemulsion. To determine the influence of ascorbic acid on the rheology of SDS/pentanol/H 2 O microemulsions, samples with 6% SDS (percentage by weight) and increasing contents of ascorbic acid were examined (along a dashed line corresponding to 6% SDS in the phase diagram) (Figure 1 (18,37) Table I).

iii )I( Ill D. VITAMIN C AND SDS/PENTANOL/WATER SYSTEM 273 0.03 ----.----........----------.-----,.-----,------...-----, 0.025 I I I I I I - - - - -- -- - - -- - , - -- - - - - I - - - -- - -- , - - - - - - I - --- - - T - -- - - - -- , - - 0.02 --2%vit.C i 0.015 • _. - 10% vit. C . .. . . . .. : ..... : .:i-_. �· � '- . B C i- - - - - -:- - . ·g CJ Cl) iii 0.01 0.005 -• 20%vit.C -X• 60%vit. C I I I "- I I ! I I llii,. I I I � : 0/W -- ____ ..!_ _______ 1 _______ 1 ____ -- -'------ _!..._ _ -- _ -- .!_ ______ -·- _ ---- __ 1_ -- --__ 1 __ -- _ -- ' I I : ... : I I .. : I ' .... ' ' ' ' ' -, I I I 'lill, ' .. ' - - ! - - - o._ ________ .,.. __ ..., _____ ...,. ______ .,... __ .,..._----111 0 10 20 30 40 50 60 70 80 90 100 Water Content in Microemulsion (Wt%) 0.03 ------------.-----.-----,.----,.-----,.----...----...-----, d) 4�°C 0.025 , I I I I l J - - , - ---- - - , - - - - - -- 1 - - - - - - - T -- - -- - - 1 -- - - - - - 1 - - - - - - - 1 - - - - - - - 0.02 f t I I I I - - -- - -- 1 - - - - -- - 1 - - - - - - - .- - - - - - - - . - --- -- - . - - - - - - -- , -- - -- - -+--no vit. C W/0: i 0.015 --2%vit.C ' ' .. • • 10% vit. C · · · · · - ·, - - - - - - -,- - - - - · 'g CJ Ill 0.01 0.005 0 -• 20%vit.C --X - 60% vit. C • 10 20 30 40 50 60 70 Water Content in Microemulsin (Wt %) Figure 4. (cont'd.) 80 90 100 All rheological measurements were conducted with a Bohlin Rheometer CVO 50 with a PC computer and thermostat RTE 111 M (Spectro-Lab). The double-gap measuring system DG 24/27 consists of a hollow cylinder, which is lowered into a cylindrical groove