[shane911]

Does increasing surfactant chain length decrease surface tension? why is that? Thank you

[shane911]

what is the orientation of surfactant molecules at liquid surface. Is it parallel? would increasing concentration change their orientation?

[argulor]

would increasing concentration change their orientation?

Yes it does. Try digging through this: http://en.wikipedia.org/wiki/Critical_micelle_concentration

[shane911]

when we try to measure surface tension of different concentrated solutions of n-butanol with a tensiometer, we have to go from lower to higher concentration and not the other way around. what is the reason for that?

[shayan825@gmail.com]

when we try to measure surface tension of different concentrated solutions of n-butanol with a tensiometer, we have to go from lower to higher concentration and not the other way around. what is the reason for that?

[Arkcon]

This seems to me to be standard way we perform any test with an instrument.  Can you think of a reason why?  What are all the steps -- do you rinse in between?  What would be the difference if you went high to low, in particular for rinsing out the last sample?