Mixing solvents, or how does paint thinner work? I would like to understand how a mixture of solvents works together.

For example, there are two solvents combined, and each one alone can dissolve some material, but one acts faster.  

How do they interact when used in combination on the same material?



An example would be paint thinner, for example a mixture of toluene and xylene.

One reason to use multiple solvents in a paint thinner is to make it dissolve more kinds of paints etc. (In German, this is called "universal thinner".)

But does the combination of multiple solvents somehow make it work better dissolving a single compound or mixture?

I had dissolved some polycaprolactone in that universal thinner above, and it seemed to dissolve quicker than in either toluene or xylene alone.
I do not know exactly what is in the thinner, so it does not mean much &ndash; but it made me wonder about this! 

So, in which ways interact multiple solvents in the context of the example, and are there other mechanisms in general, not covered by the example?



Addendum:

For discussing a simple example, let's just assume the thinner contains only the two solvents above.

But for context, I looked up the Sicherheitsdatenblatt (MSDS) for my example thinner, which shows some more solvents on the list of ingredients:

Compound                                Mass %
----------------------------------------------
Toluol                                  15- 45
Xylol                                   10- 40
Ethanol                                  2- 15 
Aceton                                   5- 20 
Ethylacetat                              5- 20 
n- Butylacetat                          10- 20
aromat. hydrocarbon mixture (C8-C10)     5- 15 
aliph. hydrocarbons (C7-C9)              2- 10
I had dissolved some polycaprolactone in that universal thinner above, and it seemed to dissolve quicker than in either toluene or xylene alone.


Some of these universal thinners do contain a lot more than just toluene and the xylenes.

If you want to find out about the composition of these mixtures, a material safety data sheet (MSDS, in German: Sicherheitsdatenblatt), provided by the manufacturer gives some information:

As an example, take this MSDS by a swiss manufacturer, which lists the following ingredients:

\begin{array}{lr}
\textrm{compound} &amp; \textrm{amount [%]}\\
\hline
\textrm{toluene} &amp; 25-50\\
\textrm{xylene} &amp; 10-25\\
\textrm{acetone} &amp; 10-25\\
\textrm{propan-2-ol} &amp; 2.5-10\\
\textrm{4-methyl-pentan-2-one} &amp; 2,5-10\\
\textrm{2-methoxy-1-methylethylacetate} &amp; 2,5-10\\
\end{array}

Particularly the latter two might be much better solvents for the polycaprolactone than toluene or xylene.